:**macrocell** A format used by Golly and its hashlife algorithm,
capable of storing repetitive patterns very efficiently, even if they
contain a large number of cells. For example, a filled square 2^{167}
cells on a side can be stored in less than three kilobytes in
macrocell format, or about 800 bytes in compressed macrocell format.
The square's total population is over a googol, 10^{100}; the number of
atoms in the observable universe is only about 10^{80}.

This high level of compression is obtained by defining a tree structure composed of increasingly large cell "tiles" with power-of-two dimensions. Tile definitions of any size are re-used whenever they appear multiple times in a large pattern (at the same power-of-two offset). For example, the following is a macrocell encoding of a complex pseudo still life arrangement of ships, with a total population over 2500 cells:

[M2] (golly 3.0) #R B3/S23 .OO.OO$O.O.O.O$OO...OO$$OO...OO$O.O.O.O$.OO.OO$ 4 0 1 1 1 5 2 0 2 2 6 3 3 0 3 7 4 4 4 4

The first line after the #R rule line defines a quadtree tile at
the lowest level - a level-3 tile in this case, meaning a 2^{3} square
area. At this level the pattern is encoded in a modified ASCII
format with dollar signs as line separators. The next line, #2,
defines a level-4 quadtree tile, made from one empty level-3 tile in
the northwest corner (0), and three copies of the level-3 tile that
was defined on the previous line (1). Lines 3, 4, and 5 similarly
define level 5, 6, and 7 quadtree tiles by giving the line numbers of
four tiles of the next lower size.

Many patterns are only moderately repetitive, so macrocell format is somewhat less successful at compressing them. Certainly most patterns are not nearly as regular as the artificial example above: there are usually many different tiles defined at each level, not just one. Chaotic patterns, such as ash from random soups, usually need so many different tile definitions that they can be stored more efficiently using rle format.

:**macro-spaceship** A self-constructing or self-supporting
spaceship, such as the Caterpillar, Centipede,
half-baked knightship, waterbear, Demonoid, Orthogonoid, and
Caterloopillar. Engineered spaceships of these types tend to be
much larger and more complex than elementary spaceships.

:**mango** (p1) An uncommon 180-degree rotationally symmetric 8-bit
still life. The acorn produces a mango as part of its ash.

.OO.. O..O. .O..O ..OO.

:**mathematician** (p5) Found by Dave Buckingham, 1972.

....O.... ...O.O... ...O.O... ..OO.OO.. O.......O OOO...OOO ......... OOOOOOOOO O.......O ...OOOO.. ...O..OO.

:**Max** A name for the smallest known spacefiller. The name represents
the fact that the growth rate is the fastest possible. (This has not
quite been proved, however. There remains the possibility, albeit
not very likely, that a periodic agar could have an average
density greater than 1/2, and a spacefiller stretching such an agar
at the same speed as the known spacefillers would have a faster
average growth rate.)

:**mazing** (p4) In terms of its minimum population of 12 this ties with
mold as the smallest p4 oscillator. Found by Dave Buckingham in
December 1973. For some constructions using mazings, see popover
and sixty-nine.

...OO.. .O.O... O.....O .O...OO ....... ...O.O. ....O..

:**megacell** = p1 megacell.

:**memory cell** A type of information storage circuit useful in many
patterns that perform complex logical operations. Most commonly a
memory cell can store a single bit of information. See for example
demultiplexer, honey bit, and boat-bit. Depending on the
application, the circuit may be a toggle circuit, or it may be
possible to send one or more signals to set the circuit to a "1"
state, as can be done with a keeper mechanism. In that case a
different input signal must be used to test the current state,
usually with a destructive read reaction.

:**metacatacryst** A 52-cell pattern exhibiting quadratic growth. Found
by Nick Gotts, December 2000. This was for some time the smallest
known pattern (in terms of initial population) with superlinear
growth. See also catacryst for more recent record-holders.

:**metacell** CA logic circuitry that emulates the behavior of a single
cell. The circuitry is hard-wired to emulate a particular CA rule,
but changing the rule is usually a matter of making simple
adjustments. Known examples include David Bell's original 500×500
unit Life cell, Jared Prince's Deep Cell, Brice Due's
OTCA metapixel, and Adam P. Goucher's megacell.

:**metamorphosis** An oscillator built by Robert Wainwright that uses
the following reaction (found by Bill Gosper) to turn gliders into
LWSS, and converts these LWSS back into gliders by colliding them
head on using an LWSS-LWSS bounce. There are two ways to do the
following reaction, because the twin bees shuttle spark is
symmetric.

...................O......... ....................O........ ..................OOO........ ............................. ............................. ............................. ............................. ............................. ............O...O.....O.OO... OO.........O.....O....O.O.O.. OO.........O.........O....O.. ...........OO...O.....O.O.O.. .............OOO......O.OO... ............................. .............OOO............. ...........OO...O............ OO.........O...............OO OO.........O.....O.........OO ............O...O............

:**metamorphosis II** An oscillator built by Robert Wainwright in December
1994 based on the following p30 glider-to-LWSS converter. This
converter was first found by Paul Rendell, January 1986 or earlier,
but wasn't widely known about until Paul Callahan rediscovered it in
December 1994.

......................O. .....................O.. .....................OOO ........................ ........................ .........O.O............ .........O..O........... OO..........OO.......... OO........O...OO........ .....OO.....OO.......... ....O....O..O........... .........O.O............ ........................ ........................ ........................ ........................ ................O....... ...............OOO...... ..............OOOOO..... .............O.O.O.O.... .............OO...OO.... ........................ ........................ ................O....... ...............O.O...... ...............O.O...... ................O....... ...............OO....... ...............OO....... ...............OO.......

:**metapixel** See metacell, OTCA metapixel.

:**methuselah** Any small pattern that stabilizes only after a long time.
Term coined by Conway. Examples include rabbits, acorn, the
R-pentomino, blom, Iwona, Justyna and Lidka. See also
ark.

:**Mickey Mouse** (p1) A name proposed by Mark Niemiec for the following
still life:

.OO....OO. O..O..O..O O..OOOO..O .OO....OO. ...OOOO... ...O..O... ....OO....

:**middleweight emulator** = MW emulator

:**middleweight spaceship** = MWSS

:**middleweight volcano** = MW volcano

:**mini pressure cooker** (p3) Found by Robert Wainwright before June
1972. Compare pressure cooker.

.....O..... ....O.O.... ....O.O.... ...OO.OO... O.O.....O.O OO.O.O.O.OO ...O...O... ...O.O.O... ....O.O.... .....O.....

:**M.I.P. value** The maximum population divided by the initial
population for an unstable pattern. For example, the R-pentomino
has an M.I.P. value of 63.8, since its maximum population is 319.
The term is no longer in use.

:**mod** The smallest number of generations it takes for an oscillator
or spaceship to reappear in its original form, possibly subject to
some rotation or reflection. The mod may be equal to the period,
but it may also be a quarter of the period (for oscillators that
rotate 90 degrees every quarter period) or half the period (for other
oscillators which rotate 180 degrees every half period, and also for
flippers).

:**mold** (p4) Found by Achim Flammenkamp in 1988, but not widely known
until Dean Hickerson rediscovered it (and named it) in August 1989.
Compare with jam. In terms of its minimum population of 12 it
ties with mazing as the smallest p4 oscillator. But in terms of
its 6×6 bounding box it wins outright. In fact, of all oscillators
that fit in a 6×7 box it is the only one with period greater than
2.

...OO. ..O..O O..O.O ....O. O.OO.. .O....

:**monochromatic salvo** A slow salvo that uses gliders of only one
colour. For example, the slow salvos generated by
half-baked knightships are monochromatic, because they are
generated by a single type of reaction which can happen at any
position along a diagonal line. The smallest possible step size is
one full diagonal (1fd), which is two half diagonals (2hd), which
means that any single glider-producing reaction can only reach half
of the available glider lanes. See colour of a glider.

:**monogram** (p4) Found by Dean Hickerson, August 1989.

OO...OO .O.O.O. .OO.OO. .O.O.O. OO...OO

:**monoparity salvo** A slow salvo that uses gliders of only one
parity. Compare monochromatic salvo.

:**Moore neighbourhood** The set of all cells that are orthogonally or
diagonally adjacent to a cell or group of cells. The von Neumann
neighbourhood of a cell can be thought of as the points at a
Chebyshev distance of 1 from that cell. Compare
von Neumann neighbourhood. The Conway's Life rule is based on the
Moore neighborhood, as are all the "Life-like" rules and many other
commonly investigated rule families.

Cell neighbourhoods can also be defined with a higher range. The
Moore neighbourhood of range *n* can be defined recursively as the
Moore neighbourhood of the Moore neighbourhood of range *n*-1. For
example, the Moore neighbourhood of range 2 includes all cells that
are orthogonally or diagonally adjacent to the standard Moore
neighbourhood.

:**moose antlers** (p1)

OO.....OO O.......O .OOO.OOO. ...O.O... ....O....

:**mosquito** See mosquito1, mosquito2. mosquito3, mosquito4 and
mosquito5.

:**mosquito1** A breeder constructed by Nick Gotts in September 1998.
The original version had an initial population of 103, which was then
the smallest for any known pattern with superlinear growth (beating
the record previously held by Jaws). This was reduced to 97 by
Stephen Silver the following month, but was then almost immediately
superseded by mosquito2.

Mosquito1 consists of the classic puffer train plus four LWSS and four MWSS (mostly in predecessor form, to keep the population down). Once it gets going it produces a new block-laying switch engine (plus a lot of junk) every 280 generations. It is therefore an MMS breeder, albeit a messy one.

:**mosquito2** A breeder constructed by Nick Gotts in October 1998. Its
initial population of 85 was for a couple of hours the smallest for
any known pattern with superlinear growth, but was then beaten by
mosquito3.

Mosquito2 is very like mosquito1, but uses two fewer MWSS and one more LWSS.

:**mosquito3** A breeder constructed by Nick Gotts in October 1998. Its
initial population of 75 was at the time the smallest for any known
pattern with superlinear growth, but was beaten a few days later by
mosquito4.

Mosquito3 has one less LWSS than mosquito2. It is somewhat different from the earlier mosquitoes in that the switch engines it makes are glider-producing rather than block-laying.

:**mosquito4** A slightly improved version of mosquito3 which Stephen
Silver produced in October 1998 making use of another discovery of
Nick Gotts (September 1997): an 8-cell pattern that evolves into a
LWSS plus some junk. Mosquito4 is a breeder with an initial
population of 73, at the time the smallest for any known pattern with
superlinear growth, but superseded a few days later by mosquito5.

:**mosquito5** A slightly improved version of mosquito4 which Nick Gotts
produced in October 1998. The improvement is of a similar nature to
the improvement of mosquito4 over mosquito3. Mosquito5 is a
breeder with an initial population of 71. At the time, this was
the smallest population for any known pattern with superlinear
growth, but it has since been superseded by teeth, catacryst,
metacatacryst, Gotts dots and wedge.

:**moving sawtooth** A sawtooth such that no cell is ON for more than a
finite number generations. David Bell constructed the first pattern
of this type, with a *c*/2 front end and a *c*/3 back end. The front end
is a blinker puffer. The back end ignites the blinker fuse. The
smallest currently known moving sawtooth has a *c*/2 front end and a
2*c*/5 back end. The front end is a bi-block puffer. The back end
ignites the bi-block fuse.

:**multiple roteightors** (p8) An extensible oscillator family
consisting of one or more roteightor rotors, discovered by Dean
Hickerson in 1990.

....................O........... ........OO........OOO........... .........O.......O.............. .........O.O.....OO............. ..........OO.............O...... .......................OOO...... ....OO........OOO.....O......... .....O.......O..O......O........ .....O.O........O..O...O......O. ......OO..O....O..O.........OOO. .........O........O..O.....O.... OO.......O..O.....OOO......OO... .O.......OOO.................... .O.O............................ ..OO....................OOO..... ...............OOO.....O..O..... ......OOO.....O..O........O..... .....O..O........O..O....O..OO.. ........O..O....O..O........O.O. ...O...O..O........O..O.......O. ...O......O..O.....OOO........OO ....O.....OOO................... .OOO....................OO...... .O......................O.O..... ........OO......OOO.......O..... .........O.....O..O.......OO.... ......OOO.........O............. ......O......O...O..OO.......... .............O......O.O......... ..............O.......O......... ...........OOO........OO........ ...........O....................

:**multiplicity** In a reflectorless rotating oscillator, the maximum
number *n* of independent patterns that can orbit a single point, in a
way that reduces the period of the combined oscillator by a factor of
*n*.

:**multi-state Life** = colourised Life

:**multum in parvo** (stabilizes at time 3933) A methuselah found by
Charles Corderman, but not as long-lasting as his acorn.

...OOO ..O..O .O.... O.....

:**muttering moat** Any oscillator whose rotor consists of a closed
chain of cells each of which is adjacent to exactly two other rotor
cells. Compare babbling brook. Examples include the bipole, the
blinker, the clock, the cuphook, the Gray counter, the
quad, the scrubber, the skewed quad and the p2 snake pit. The
following diagram shows a p2 example (by Dean Hickerson, May 1993)
with a larger rotor. See ring of fire for a very large one.

OO..... O.O.OO. .....O. .O..O.. ..O.... ..O.O.O .....OO

:**MW emulator** (p4) Found by Robert Wainwright in June 1980. See also
emulator and filter.

.......O....... ..OO.O...O.OO.. ..O.........O.. ...OO.....OO... OOO..OOOOO..OOO O..O.......O..O .OO.........OO.

:**MWSS** (*c*/2 orthogonally, p4) A middleweight spaceship, the third most
common spaceship. Found by Conway in 1970 by modifying a LWSS.
See also HWSS.

...O.. .O...O O..... O....O OOOOO.

The MWSS possesses both a tail spark and a belly spark which can easily perturb other objects as it passes by. The spaceship can also perturb some objects in additional ways. For examples see blinker puffer and glider turner.

Dave Buckingham found that the MWSS can be synthesized using three gliders, and can be constructed from two gliders and another small object in several more ways. Here is the three-glider synthesis:

...........O.. ...........O.O ...........OO. .............. .............. .O......OO.... .OO.....O.O... O.O.....O.....

:**MWSS emulator** = MW emulator

:**MWSS out of the blue** The following reaction, found by Peter Rott in
November 1997, in which a LWSS passing by a p46 oscillator
creates a MWSS travelling in the opposite direction. Together with
some reactions found by Dieter Leithner, and a LWSS-turning reaction
which Rott had found in November 1993 (but which was not widely known
until Paul Callahan rediscovered it in June 1994) this can be used to
prove that there exist gliderless guns for LWSS, MWSS and HWSS
for every period that is a multiple of 46.

O..O................................. ....O................................ O...O................................ .OOOO................................ ..................................... ..................................... ..................................... ..................................... ..................................... ...................OO..............OO ..................OO...............OO ...................OOOOO............. ..OO................OOOO............. ..OO.....O........................... ........OOO.........OOOO............. .......O.O.O.......OOOOO............. ........O..O......OO...............OO ........OOO........OO..............OO .........O........................... ..................................... ..................................... ..................................... ..................................... ..O.......O.......................... ..................................... OOO.......OOO........................ .OO.OO.OO.OO......................... ..OOO...OOO.......................... ...O.....O........................... ..................................... ..................................... ..................................... ..................................... ..................................... ..................................... ..................................... ..................................... ..................................... ..................................... ..OO.....OO.......................... ..OO.....OO..........................

:**MWSS-to-G** See 135-degree MWSS-to-G, 45-degree MWSS-to-G.

:**MW volcano** (p5) Found by Dean Hickerson in April 1992.

......O...... ....O...O.... ............. ...O.....O... .OOO.OOO.OOO. O...OO.OO...O O.OOO.O.OOOO. .O........... ...O.O.O.OO.O ..OO.OOO.O.OO ...O.O..O.... ...O..OO..... ..OO.........

:**My Experience with B-heptominos in Oscillators** An article by Dave
Buckingham (October 1996) available from
http://conwaylife.com/ref/lifepage/patterns/bhept/bhept.html. It
describes his discovery of Herschel conduits, including sufficient
(indeed ample) stable conduits to enable, for the first time, the
construction of period *n* oscillators and true period *n* guns for
every sufficiently large integer *n*. See Herschel loop and emu.