#Life 1.05 #R 012345678/3 #D This pattern shows the two clean blocking collisions which arise. #D If we label the lower one as (0,0), the upper one is (2,1) since the #D head of its horizontal ladder has an identical shape but is two cells #D further to the left, while it has opposite parity with respect to the #D boundary of the vertical ladder. #D #D (There are also two 'dirty' collisions, which create small transient #D eruptions of lava, but these are not needed for our purposes.) #D Note that the final fates of the two collisions are mirror images; #D this is a consequence of the head's flip symmetry after half a cycle. #D #D David Griffeath and Cris Moore ....................................................** ....................................................**** .....................................................*** ....................................................****** ....................................................*.**** 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