The boojum reflector is a 180° glider reflector found by Dave Greene in April 2001 as a modification of Paul Callahan's Herschel receiver, 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The boojum reflector was both the smallest and fastest known stable reflector, until it was superseded by the rectifier in 2009 and the Snark in 2013.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:
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.
- ↑ 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.