the three B - C collisions

**Figure 3.12:** B and C gliders, when the C tile is in the ``upper T1'' [C1] alignment, displace the C stack leftwards by four cells.
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**Figure 3.13:** B and C gliders, colliding when the C stack is in the ``lower T1'' [C2] alignment, metamorphose into a D glider, moving right at 1/5 c as shown in the left panel. When the stack is in the ``T3'' [C3] alignment, the result is an E glider, moving left at 1/4 c, as seen in the right panel.
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