Highway robber

A highway robber is any mechanism that can retrieve a signal from a spaceship lane while allowing spaceships on nearby lanes (even those a single lane away) to pass by unaffected. In practice the spaceship is generally a glider. The spaceship is removed from the lane in question, an output signal is generated elsewhere, and the highway robber returns to its original state. A competent highway robber does not affect spaceships even on the lane adjacent to the affected spaceship stream, except perhaps during the highway robber's recovery period.

A stable highway robber with repeat time 878 was assembled by Chris Cain in 2015, with an update by Entity Valkyrie in January 2019 to simplify the extraction of the output signal. A simpler highway robber with improved clearance and repeat time 876 was constructed by Louis-François Handfield in May 2020, with subsequent improvements made by Goldtiger997. The next version made use of the Bandersnatch to reduce the repeat time to 863 ticks. On June 23, Goldtiger997 posted a larger staged recovery highway robber with a repeat time of 742 ticks. A variant of this mechanism that allows for bounding box reduction was later assembled.

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A stable highway robber with 742-tick repeat time, allowing gliders to pass by on the same lane 47+ ticks after the activating glider. There are three possible glider outputs, but two of them are awkwardly close to other glider lanes. (click above to open LifeViewer) RLE: here Plaintext: here

A related but slightly different topic is to find a stable edgy eater with maximum clearance. The hypothetical device does not have to emit output signal(s), but it is expected to have a relatively small repeat time of less than 100. Existing methods such as tub-with-tail eater, sidesnagger and 7×9 eater do not qualify as solutions, because they cannot handle a glider immediately adjacent (1hd away) to the working input lane. Currently, whether such a pattern exists is still an open problem.

External links

• Highway robber at the Life Lexicon
• Highway robber challenge (discussion thread) at the ConwayLife.com forums
• How about a direct highway robber? (discussion thread) at the ConwayLife.com forums
• Smaller "Highway Robber" at Game of Life News. Posted by Dave Greene on March 14, 2009.