Cook's F-glider, backward velocity -c/9

Cook remarks that the F glider can be triggered from an A-C collision, the details of which are shown in Section 3.2.2.

**Figure 2.29:** The lackadasical F glider, which moves 4 left in 36 generations, for a velocity of -1/9 c. Left: the unit cell, expressed with T tiles. Right: presentation with S tiles, showing the different approach aspects. F gliders can be overpacked just as well as EBar gliders, but no such arrangement can arise from natural evolution.
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One period of an F glider occupies six ether files on the left, such as would be used in the approach of an A glider. However, it occupies only four files on the right, the path along which a B would approach. The difference is due, of course, to the differences in velocity between A's and B's, given that their orientations relative to the ether are different.