Minecraft wiki entry for Piston, associated text: Comparable size and speed to some of the basic redstone IMPLIES gate. This gate represents material implication. Returns false only if the implication A → B is false. That is, if the conditional A is true, but the consequent B is false. It is often read "if A then B." It is the logical equivalent of "B or NOT A". The torch under the mobile block is in a hole.