One of the blocks is hit by a glider, triggering a pi-heptomino, and the diagonally opposite block catalyses it to release a glider and drop a block 6 cells away. The remaining block is not touched, but it is exactly aligned with the newly laid block, effectively mirroring the constellation vertically. A second glider can be sent in at a different lane, at least 235 ticks later, to perform the same reaction and restore the original pattern.
Interestingly, the precise arrangement of blocks arise from a collision between a glider and a half-blockade, as reported by Dave Filpus in 1973.[4] This results in a 4-glidersynthesis for the arrangement.
