Boojum reflector

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Boojum reflector
x = 44, y = 32, rule = B3/S23 4bobo6b2o$5b2o6b2o$5bo7$40bo$39bobo$39bobo$20b2o16b2ob2o$20b2o$38b2ob 2o$2b2o34b2obo$bobo39bo$bo40b2o$2o2$34b2o$34b2o4b2o$11b2o27bobo$10bobo 29bo$10bo31b2o$9b2o23b2o$34b2o3$29bo$28bobo$29bo! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ AUTOSTART ]] #C [[ HEIGHT 400 THUMBSIZE 2 ZOOM 10 GPS 20 LOOP 240 ]]
Pattern type Stable reflector
Number of cells 60
Bounding box 44 × 32
Angle 180°
Repeat time 202
Colour Colour-preserving
Discovered by Dave Greene
Year of discovery 2001

The boojum reflector is a 180° glider reflector found by Dave Greene in April 2001 as a modification of Paul Callahan's Herschel receiver,[1] winning $100 bounties offered by Alan Hensel and Dieter Leithner. The name is taken from Lewis Carroll's The Hunting of the Snark, referring to the fact that a small 90-degree stable reflector was really what was wanted.[note 1]

The boojum reflector was both the smallest and fastest known stable reflector, until it was superseded by the rectifier in 2009 and the Snark in 2013.

The boojum reflector produces an unwanted beehive, which is then deleted by a later glider. If the beehive is removed before the latter glider hits it, the glider will leave the reflector. This reaction can be seen in this p226 glider shuttle:

x = 76, y = 50, rule = B3/S23 15bo$14bobo$15bo3$9b2o$9b2o23b2o$b2o31bo$2bo29bobo$2bobo27b2o$3b2o4b2o $9b2o2$43b2o$43bo$41bobo$3bob2o34b2o$b3ob2o$o22b2o19b2o$b3ob2o16b2o11b o7b2o$3bobo31bo$3bobo29b3o$4bo4$52b2o$44b2o5b2o18bo$43bo2bo7bo15bobo$ 38b2o4b2o4bo2bo16bobo$30b2o5b2o14b2ob3o10b2ob3o$30b2o7bo13b5obo15bo$ 50b2o6b3o8b2ob3o$33b2o17bo5b2o9b2obo$32bobo18bo2bob2o$32bo19b2ob5o$31b 2o18bob2o2b3o$51bobo$51bo13b2o$65b2o4b2o$42b2o6b3o18bobo$41bobo29bo$ 41bo31b2o$40b2o23b2o$65b2o3$60bo$59bobo$60bo! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ WIDTH 840 HEIGHT 560 THUMBSIZE 2 ZOOM 10 GPS 20 AUTOSTART LOOP 226 ]]
p226 glider shuttle
(click above to open LifeViewer)
RLE: here Plaintext: here

A different type of Boojum shuttle is possible by switching the output gliders and the beehive deleting gliders. The corresponding beehive-glider collision does not become nothing by itself, but the block from that boojum serves as a catalyst for the successful removal.

x = 73, y = 51, rule = B3/S23 14bo$13bobo$14bo3$8b2o$8b2o23b2o$2o31bo$bo29bobo$bobo27b2o$2b2o4b2o$8b 2o2$42b2o$2o40bo$o39bobo$2bob2o34b2o$b2ob2o$22b2o$b2ob2o16b2o18b2o$2b obo37b2o$2bobo25bo$3bo25b2o$29bobo4$41bobo$42b2o25bo$42bo25bobo$29b2o 37bobo$29b2o18b2o16b2ob2o$49b2o$67b2ob2o$31b2o34b2obo$30bobo39bo$30bo 40b2o$29b2o2$63b2o$63b2o4b2o$40b2o27bobo$39bobo29bo$39bo31b2o$38b2o23b 2o$63b2o3$58bo$57bobo$58bo! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ WIDTH 840 HEIGHT 560 THUMBSIZE 2 ZOOM 10 GPS 20 AUTOSTART LOOP 225 ]]
(click above to open LifeViewer)
RLE: here Plaintext: here


  1. 180-degree reflectors have limited use in larger circuitry constructions because they cannot get a glider to wherever it needs to be. A composite 180-degree reflector can be made from two 90-degree reflectors.


  1. Dave Greene (December 9, 2020). Re: History Of ConwayLife (discussion thread) at the forums

External links