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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the production of reproducible
recordings of video or other signals, and more particularly is directed to
methods for producing such recordings by optical means.
2. Description of the Prior Art
The disc recording of audio signals is well known, and involves the use of
a lacquer disc for the original recording. Such original lacquer disc,
usually constituted by an aluminium base plate with a coating of acetate
plastic thereon, is placed on a recording turntable which is rotated at a
suitably slow standard speed, for example, 331/3, 45 or 78 r.p.m. During
such rotation of the lacquer disc, a cutter including an electromechanical
transducer and a cutting stylus is driven in the radial direction of the
turntable by means of a lead screw so that the cutting stylus cuts a
spiral groove in the record. As the spiral groove is being cut, electrical
signals corresponding to the audio or sound signals to be recorded are
applied to a driving coil of the cutter transducer for effecting
corresponding vibrations of the cutting stylus with the result that
undulations are formed in the spiral groove to represent the recorded
signals. In mass producing phonograph record discs from such original
lacquer disc, the latter is metalized and then electroplated, whereupon
the plating is separated from the lacquer and reinforced by backing with a
solid metal plate to produce the so-called master which is, in turn
electroplated. Thereafter, by well known steps, a mother and then a
stamper are produced from the master. Stampers containing the audio
signals to be recorded in the opposite sides of the final phonograph
record are then mounted in the upper and lower jaws of a hydraulic press,
and a preform or biscuit of thermoplastic material is placed between the
two stampers which are heated and pressed towards each other by closing of
the jaws of the press. When an impression of the stampers has been
obtained in the thermoplastic material, the stampers are cooled so as to
cool and set the resulting plastic phonograph record therebetween.
Finally, the jaws of the press are opened and the phonograph record is
removed from the press with the modulated grooves in each face of such
record corresponding to those in the respective original lacquer disc. In
reproducing the audio signls thus recorded the phonograph record disc is
placed on a turntable so as to turn at a constant rotational speed
corresponding to that at which the recording turntable was rotated during
the production of the original lacquer record. A pick-up is made to track
the spiral groove in the phonograph record disc by means of a stylus or
needle depending from the pick-up, and the undulations in the groove cause
vibrations of the stylus or needle with the result that the pick-up
transducer generates an output voltage corresponding to the audio signals
represented by the undulations in the groove. Such output of the pick-up
transducer, after suitable amplification and equalization, may be employed
to drive a loudspeaker which provides an audible reproduction of the
recorded sound.
It has also been proposed to record video signals on a record disc by a
method similar to that described above for the recording of audio signals.
If the resulting video record disc has one frame of the video signals
recorded in each turn of its spiral groove, it will be necessary, during
reproducing of the recorded video signals, to rotate the video record disc
at a high speed, for example, 1,800 r.p.m. in the case of NTSC video
signals. It will be apparent that, by reason of such high speed rotation
of the video record disc, various technical difficulties will be
encountered in reproducing the video signals recorded in the spiral groove
of the record disc by means of a pick-up or transducer having a stylus
which tracks the groove. Even though such technical difficulties involved
in the reproducing of the recorded video signals may be overcome, the
recording of the video signals by mechanical cutting of the groove in the
original or lacquer record, as described above in the case of the
recording of audio signals, cannot be effected with the original or
lacquer record being rotated at the high speed of 1,800 r.p.m. If the
original or lacquer record is rotated at such a high speed, the cutting
stylus is burned by the intense heat generated as a result of the friction
between the cutting stylus and the original lacquer record and, further,
it is extremely difficult to provide the cutting stylus and transducer
with the requisite high-frequency characteristics. Therefore, in practice,
the recording of video signals by the mechanical cutting of an original
lacquer record is carried out with the recording turntable being rotated
at a speed which is about 1/20th the rotational speed to be used when
reproducing the recorded video signals. Therefore, if a video record disc
is to be provided with a playing time of 10 minutes, more than three hours
will be required for the recording of the corresponding original lacquer
record. Furthermore, if the original lacquer record is rotated at a
relatively slow speed during the cutting of the groove therein, that is,
during the recording process, video signals cannot be directly applied to
the cutting transducer from a television camera or other video signal
source, and it is necessary to provide a frequency converter between the
signal source and the recording apparatus. Such frequency converter may
employ an intermediate recording medium which is driven at a standard high
speed during the recording thereon of the video signals from the
television camera or other source, and is then driven at a relatively slow
speed during the reproducing of the video signals from the intermediate
recording medium for feeding to the recording apparatus by which the video
signals are recorded as undulations or irregularities in the groove being
mechanically cut in the original lacquer record during the relatively slow
rotation thereof. Obviously, the long period of time required for the
recording of video signals and the need to employ a frequency converter,
as aforesaid, are serious disadvantages of the existing method for
producing video record discs.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
improved method of producing a reproducible recording of video or other
signals, and which avoids the above mentioned disadvantages of the
existing methods therefor.
More specifically, it is an object of the invention to provide a method for
producing a reproducible recording of video or other signals while
simultaneously forming a tracking path associated with the recorded
signals, and in which the video or other signals may be recorded as
received from a source thereof, for example, a television camera.
Another object is to provide a method for optically producing a
reproducible recording of video or other signals together with an
associated tracking path on a photosensitive record medium from which
numerous copies or records can be conveniently mass produced.
Still another object is to provide a method of producing a reproducible
recording of video or other signals by employing such signals for
modulating the intensity of a laser light beam which suitably scans the
surface of a photo-sensitive record medium so as to form a tracking path,
for example, in the form of a spiral groove, in which the recorded signals
are defined by undulations or irregularities in such tracking path.
In accordance with an aspect of this invention, the intensity of at least
one laser light beam is modulated by the video or other signals to be
recorded while such light beam scans a substantially flat surface on a
photo-sensitive record medium which is photo-reacted to a degree varying
substantially linearly in correspondence with the intensity of the light
impinging thereon over a predetermined range of light intensities, and the
intensity of the light beam and the degree of modulation thereof by the
signals being recorded are selected to maintain the maximum and minimum
intensities of the modulated light beam within such predetermined range.
The above, and other objects, features and advantages of the invention,
will be apparent from the following detailed description of illustrative
embodiments which is to be read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating the essential components of an
apparatus that may be employed in practicing the method according to this
invention for optically producing a reproducible recording of video or
other signals;
FIG. 2 is a graph illustrating the photo-sensitive characteristics of two
photo-resist materials that may be employed as the photo-sensitive record
mediums in practicing the method according to this invention;
FIG. 3 is a schematic view illustrating the elements of a light modulator
that may be employed in the apparatus of FIG. 1;
FIG. 4 is a graph showing the modulating characteristics of the light
modulator of FIG. 3, and to which reference will be made in explaining the
operation thereof;
FIG. 5 shows a graph of the photo-sensitive characteristics of a record
medium in association with diagrammatic illustrations of the intensity of
a modulated light beam and of the resulting signal recording and tracking
path, and to which reference will be made in explaining the optical
recording method according to this invention; and
FIGS. 6A and 6B are schematic views illustrating other respective
embodiments of the method according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in detail, and initially to FIG. 1 thereof, it
will be seen that a recording apparatus 10 that may be used for practicing
the method according to an embodiment of this invention generally
comprises a laser light source 11 which emits a laser light beam 12 having
a predetermined light intensity. The laser light beam 12 is directed
through a light modulator 13 for modulating the intensity of the laser
light beam in accordance with the signals to be recorded which are
received by light modulator 13 through a compensation circuit 14 from a
signal source 15, for example, a television camera. The compensation
circuit 14 compensates for non-linearity in the photo-sensitive
characteristics of the record medium, which is hereinafter described in
detail, and in the modulation characteristics of the light modulator 13.
The modulated laser light beam issuing from light modulator 13 is passed
through a speed compensating filter 16 and then projected by a condensing
lens 17 onto the substantially flat surface of a photo-sensitive record
medium 18.
As shown, the record medium 18 may be conveniently in the form of an
original record disc constituted by a layer 19 of photo-sensitive material
coated on the surface of a glass disc or base plate 20 and having uniform
thickness of about 1 micron. The disc 20 is fixed, at its center, on a
shaft 21 which is rotated, for example, by an electric motor (not shown).
Simultaneously with the rotation of shaft 21, and hence of the original
record disc 18, the record disc 18 and laser light beam 12 are moved
relative to each other in the radial direction of the original record
disc, for example, the shaft 21 may be progressively moved in the
direction of the arrow 22 by a conventional lead screw mechanism (not
shown), so that the laser light beam 12 scans a spiral path on the surface
of photo-sensitive layer 19.
It will be apparent that even though original record disc 18 is rotated at
a constant speed, for example, 1,800 r.p.m. when recording NTSC video
signals so as to record one frame of such video signals during each
revolution of the original record disc, the linear speed of the surface of
photo-sensitive layer 19 varies over the radial extent of such surface
from a minimum speed adjacent to the axis of rotation of original record
disc 18 to a maximum speed at the outer periphery of such record disc.
Thus, even if it is assumed that the laser light beam 12 is of constant
intensity, the amount of light projected on a unit area of the
photo-sensitive layer 19 disposed close to the axis of rotation would be
substantially greater than the amount of light projected on a similar unit
area of the photo-sensitive layer disposed adjacent the outer periphery of
the original record disc 18. However, in the apparatus 10 shown on FIG. 1,
the speed compensating filter 16, which may be in the form of a gray
scale, is suitably controlled in accordance with the movement of the
original record disc 18 in the direction of the arrow 22 relative to the
laser light beam 12 so as to progressively reduce the intensity of the
laser light beam as the latter is directed against the surface of
photo-sensitive layer 19 at locations that are progressively closer to the
axis of rotation of the original record disc. Thus, the effect of the
varying linear speed at the surface of the photo-sensitive layer 19 is
substantially eliminated.
The photo-sensitive layer 19 of the original record disc 18 used in the
method according to this invention may be of a photo-resist material, such
as, for example, the negative-type photo-resist material available under
the trade name KOR from the Eastman Kodak Company and containing
polycinnamicvinyl as a major constituent thereof, or the positive-type
photo-resist available under designation AZ-1350J from the Shipley
Company, and which contains novolac resin as a major constituent thereof.
The photo-sensitive characteristics of such negative-type and
positive-type photo-resist materials are represented by the curves 23 and
24, respectively, on FIG. 2. On FIG. 2, the amount of light projected on a
unit area of a photo-resist layer by a laser light beam having a
wavelength of 4,579 Angstroms is represented by the abscissa, while the
degree to which the photoresist layer is light- or photo-reacted is
indicated by the ordinate as the depth of photo-resist material which
remains after developing in the case of the negative-type photo-resist, or
which is removed upon developing in the case of the positive-type
photo-resist.
It will be seen that each of the characteristic curves 23 and 24 has an
inclined portion indicating that when the amount of light received by the
corresponding photo-resist material is varied in the range corresponding
to such inclined portion of the characteristic curve, the degree to which
the respective photoresist material is photo-reacted will be
correspondingly varied. After the photo-resist layer has been exposed to
light, such layer is conventionally developed. In the case of the
negative-type photoresist layer having the characteristic curve 23,
developing of such photo-resist layer after its exposure to light results
in the removal of the unexposed portions of the layer while the light- or
photo-reacted portion remains more or less undissolved in dependence on
the degree or extent to which such portion has been photo-reacted. On the
other hand, in the case of the positive-type photo-resist layer having the
characteristic curve 24, developing of such layer after its exposure to
light results in the light- or photo-reacted portion of the layer being
dissolved or removed to a depth in dependence on the degree to which such
layer was photo-reacted, while the portions of the layer which were not
exposed to light remain undissolved by the developing process. It is to be
understood that either the negative-type photo-resist material or the
positive-type photo-resist material can be employed as the photo-sensitive
layer 19 of the original record disc 18 used in practicing the method
according to this invention.
Referring now to FIG. 3, it will be seen that the light modulator 13 of the
recording apparatus 10 may include a polarizer 25, a quartz wavelength
plate or phase controller 26, an electro-optic crystal 27 and an analyzer
28 which are successively arranged in the order named in the path of the
laser light beam 12. The electro-optic crystal 27 may be a crystal of
lithium niobate, lithium tantalate or the like which exhibits the
electro-optic or Pockels effect, and is connected to an input terminal 29
at which the video or other signals to be recorded are received from
source 15 after compensation thereof in the circuit 14. Further, the
polarizer 25 and analyzer 28 are in the condition of orthogonal nicol
relative to each other so that, as is known, the intensity of the laser
light beam issuing from modulator 13 can be made to correspond to the
signal voltage being applied to electro-optic crystal 27. More
particularly, as shown on FIG. 4, if the polarizer 25 and analyzer 28 are
in the condition of orthogonal nicol relative to each other, the intensity
I of the laser light beam at the output of modulator 13 will be
proportional to sin KV, as represented by the modulation curve 30 on FIG.
4, and in which K is a constant and V is the signal voltage applied to the
electro-optic crystal 27. If the signal voltage is applied to the crystal
27 with a D.C. level V.sub.B corresponding to the point A on the
modulation curve 30, and which is selected as the operating point of
modulator 13, and if the signal voltage applied to crystal 27 varies about
such selected operating point between the limits V.sub.B1 and V.sub.B2,
for example, as indicated by the signal voltage curve 31 on FIG. 4, then
the intensity of the laser light beam at the output of modulator 13 which
is indicated by the curve 32 will be modulated in correspondence with the
signal voltage 31. The operating point A on the modulating curve 30 may be
established for the modulator 13 either by applying the corresponding
predetermined DC voltage V.sub.b to terminal 29 in addition to the signal
voltage from source 15, or the quartz wavelength plate or phase controller
26 may be selected to provide the light passing therethrough with a phase
corresponding to such DC voltage V.sub.B. Such alternative methods of
establishing the operating point A are possible as the electro-optic
effect involves the modulation of refractive index and, hence, the phase
modulation of the light.
As previously mentioned, if the photo-sensitive layer 19 of the record
medium or original record disc 18 is formed of a positive-type
photo-resist having a photo-sensitive characteristic as represented by the
curve 24 on FIG. 2 and the modulated laser light beam scans a spiral path
on the surface of such layer 19, then a reduced thickness of the
photo-sensitive layer 19 will remain along such spiral path after the
developing of the positive-type photo-resist. Thus, upon development of
the positive-type photo-resist forming the layer 19 following its exposure
to the modulated laser light beam 12 along a spiral path on the surface of
layer 19, a corresponding spiral groove will be formed in such surface
with the depth of the spiral groove at locations along the length of the
latter varying in accordance with the intensity of the modulated laser
light beam when impinging at the respective locations along the spiral
path scanned by such light beam.
It will be seen that the photo-sensitive characteristic curve 24 (FIG. 2)
for the positive-type photo-resist and a corresponding characteristic
curve 33 (FIG. 5) representing the thickness of such photo-resist
remaining after development thereof, have respective inclined portions in
which the degree to which the photo-resist is photo-reacted, and
consequently the thickness of the photo-resist remaining after
development, respectively vary substantially linearly in correspondence
with the intensity of the modulated laser light beam over a predetermined
range of light intensities.
In accordance with this invention, the intensity I of the laser light beam
12, in the absence of any modulation thereof by the video or other signals
to be recorded, is selected to correspond to the point B on curve 33 (FIG.
5) which lies on the relatively straight inclined portion of such curve,
and the degree of modulation of the intensity of the laser light beam 12
by the video or other signals to be recorded is selected so that the
minimum and maximum values I.sub.1 and I.sub.2 of the modulated intensity
of the laser light beam, represented by the curve 34 in FIG. 5, will be
within the range of light beam intensities for which there is a
substantially linear relationship between the light intensity and the
thickness of the photo-resist layer 19 remaining after the development
thereof. Thus, the groove G formed in the photo-resist layer 19 following
the development thereof will have a nominal depth d corresponding to the
point B on curve 33, that is, corresponding to the intensity of the
unmodulated laser light beam, and the depth of the groove will vary
between the minimum and maximum depths d.sub.1 and d.sub.2 corresponding
to the minimum and maximum intensities I.sub.1 and I.sub.2, respectively,
of the modulated laser light beam.
Therefore, in the developed positive-type photo-resist layer 19 of original
record disc 18, the recorded video or other signals will be accurately
represented by the undulations or irregularities S formed at the bottom of
groove G in correspondence to the varying depth of such groove.
Correspondingly, prior to the development of the photo-resist layer
forming the photo-sensitive recording medium in the embodiment of the
invention being here described, the exposure of the photo-resist layer to
the modulated laser light beam will result in the photo-reacting of the
photo-resist layer along a spiral path so as to define a tracking path
portion, with the degree to which the photo-resist layer is photo-reacted
along such spiral path being varied accurately in accordance with the
varying intensity of the modulated laser light beam so as to define a
recorded signal portion which is unified with the tracking path portion.
In a particular example of the above described method according to this
invention, the photo-sensitive layer 19 of the original record disc 18 was
constituted by the positive-type photo-resist available under the
designation AZ-1350J and had a thickness t of 1.0 micron, and the original
record disc 18 was rotated at a speed of 1,800 r.p.m. for the recording
thereon of one frame of NTSC video signals during each revolution of disc
18. In such example, the original or unmodulated intensity of the laser
light beam 12 and the degree of modulation of the laser light beam
intensity in response to the video signals were selected to provide the
minimum and maximum intensities I.sub.1 and I.sub.2 of the modulated laser
light beam with values of 77 milliwatts and 98 milliwatts, respectively.
Further, with the laser light beam 12 having a wavelength of 4,579
Angstroms and being focused by condensing lens 17 so as to impinge on the
surface of layer 19 at a beam spot having a diameter 3 to 4 microns, it
was found that the groove G resulting from development of the exposed
photo-resist layer 19 had a width substantially corresponding to the
diameter of the beam spot and a nominal depth d of 0.5 microns, with the
actual depth of the groove varying accurately in accordance with the video
signals being recorded between a minimum depth d.sub.1 of 0.2 microns and
a maximum depth d.sub.2 of 0.8 microns.
After the positive-type photo-resist layer 19 has been developed, the
original record disc 18 can be employed for the mass production of large
numbers of corresponding video record discs by a procedure similar to that
previously described for the mass production of phonograph record discs
from an original lacquer record. Each of the resulting video record discs
thus mass produced can have the recorded video signals reproduced
therefrom by means of a piezo-electric pick-up or other electro-mechanical
transducer provided with a stylus tracking the spiral groove and being
mechanically actuated by the undulations or irregularities at the bottom
of such groove which represent the recorded video signals so as to cause
the transducer to generate a corresponding electrical output. Of course,
in reproducing the video signals recorded in a video record disc produced
by the method according to this invention, the recorded video signals may
be detected optically, for example, by a laser or other light beam which
is made to track the spiral groove and which is variously reflected by the
undulations or irregularities provided at the bottom of such groove to
detect the recorded video signals, or such recorded video signals may be
detected as variations in electrostatic capacitance.
In another specific example of this invention, the negative-type
photo-resist material available commercially under the trade name KOR was
employed as the photo-sensitive layer 19 of original record disc 18, and
the unmodulated intensity of the laser light beam 12 and the degree of
modulation thereof by the video signals to be recorded were selected so
that the minimum and maximum intensities of the laser light beam impinging
on the surface of the photoresist layer were 1 milliwatt and 2 milliwatts,
respectively. With all other parameters of the method being the same as
previously described for the method employing the positive-type
photo-resist, the negative-type photo-resist layer, after development, was
found to have a spiral ridge extending from its surface with the width of
such ridge being approximately 3 microns, and with the height of the ridge
corresponding accurately to the recorded video signals and varying between
a minimum height of 2 microns and a maximum height of 8 microns. In mass
producing video record discs from the last mentioned original record disc,
the surface of the developed negative-type photo-resist may be metalized
and then electroplated for directly obtaining the so-called master from
which a mother and then a stamper may be produced in turn by the usual
techniques involved in the mass production of phonograph record discs. The
video record discs mass produced from the stamper corresponding to the
original record disc having a negative-type photo-resist as its
photo-sensitive layer may have the video signals recorded therein
reproduced in the same way as has been described above in connection with
the video record discs produced from an original record disc having a
positive-type photo-resist as its photo-sensitive layer.
Although positive- and negative-type photo-resist materials have been
specifically described above as being suitable to form the photo-sensitive
layer 19 of the record medium or disc 18 employed in the method embodying
this invention, other photo-sensitive record mediums may be similarly
used. For example, the photo-sensitive record medium may be formed of a
sublimate material, such as, lead iodide, tungsten oxide or germanium
sulfide. Such sublimate materials produce a vaporific photo-reacted
substance as a result of heat generated by the absorbtion of light.
Moreover, the mentioned sublimate materials have a very large
photo-absorbtion coefficient so that, if the thermal diffusion therefrom
is small, vaporization of the sublimate material proceeds from the surface
thereof in the direction of the depth of the layer of sublimate material
in accordance with the intensity of the modulated laser light beam which
scans the original record disc or record medium. Thus, an original record
disc having a sublimate material as the photo-sensitive layer 19 thereon
produces an end result similar to that achieved when the photo-sensitive
layer is constituted by a positive-type photo-resist, as described above.
The photo-sensitive record medium 19 of an original record disc employed in
the method according to this invention may also be constituted by a
photo-thermoplastic material, such as, for example, a photo-thermoplastic
material constituted by a first layer formed of a mixture of
diphenylsilicone and polyphenyleneoxide deposited on the surface of the
glass disc 20 and a second or outer layer formed of a mixture of
trinitrofluorenone and polyvinylcarbinol deposited over the first layer.
The laser light source 11 is selected, for example, from among krypton,
helium-cadmium and argon lasers, so as to produce a laser light beam
having characteristics that desirably correspond to the sensitivity of the
selected photo-sensitive material employed as the record medium.
Furthermore, in place of the electro-optic crystal employed in the above
described light modulator 13, the intensity modulation of the laser light
beam in accordance with the signals to be recorded may be effected by
making use of the light defraction effect produced by an ultrasonic wave.
In producing a contoured a tracking path, i.e. a groove or ridge, in, or on
the surface of the photo-sensitive layer 19 of original record disc 18, as
described above, the intensity distribution across the laser light beam
may be suitably varied, for example, by means of a lens, filter or the
like, so as to provide the resulting groove or ridge with a rectangular,
parabolic, triangular or other desired cross-sectional configuration.
In the above described embodiments of this invention, only a single laser
light beam has been employed for producing the tracking path portion and
the recorded signal portion on the original record disc 18. However, as
shown schematically on FIGS. 6A and 6B, two or more light beams can be
used for producing the tracking path portion and the recorded signal
portion on the photo-sensitive record medium. More specifically, in the
embodiment of FIG. 6A, a first laser light beam 12a of constant intensity
is reflected against the surface of the photo-sensitive record medium 18
by a semi-reflecting mirror 35 so as to produce the tracking groove or
ridge of the record medium. A second laser light beam 12b is passed
through a light modulator 13 so as to have its intensity modulated by
means of the video or other signals applied to the modulator, whereupon
the modulated laser light beam 12b is reflected by a mirror 36 so as to
pass through the semi-reflecting mirror 35 and be combined with the beam
12a of constant intensity. Thus, the light energies of the beam 12a of
constant intensity and of the modulated beam 12b are added together with
the modulated beam 12b determining the variations in the depth of the
groove or the height of the ridge that is eventually formed on the record
medium.
Referring now to FIG. 6B, it will be seen that the method according to the
present invention may also be employed for recording a plurality of
signals in the photo-sensitive record medium 18 simultaneously with the
forming of a tracking groove or ridge thereon. More specifically, in the
embodiment of FIG. 6B a laser light beam 12a of constant intensity is
directed against the surface of the photo-sensitive record medium 18 by
the semi-reflecting mirror 35, and three additional laser beams 12b.sub.1,
12b.sub.2 and 12b.sub.3 are passed through respective light modulators
13.sub.1, 13.sub.2 and 13.sub.3 having respective signals applied thereto
for modulating the intensities of the respective laser light beams. The
intensity modulated beams 12b.sub.1, 12b.sub.2 and 12b.sub.3 are
respectively reflected by semi-reflecting mirrors 35.sub.1 and 35.sub.2
and by a mirror 36 so as to be combined with the beam 12a of constant
intensity. Thus, in the method illustrated by FIG. 6B, the beam 12a of
constant intensity determines the groove or ridge formed on the
photo-sensitive record medium 18, while the intensity modulated beams
12b.sub.1, 12b | | |
