Reversive

Two predicates P and Q are said to be reversives iff they describe change in opposite directions, relative to some reference point R; if both P and Q take place (to the same extent), the change brought about by one predicate is undone by the other.


 * Illustration
 * P = enter; P denotes a change of state from S1 (x is outside) to S2 (x is inside)
 * Q = leave; Q denotes a change of state from S2 (x is inside) to S1 (x is outside)
 * 1) John entered the house (S1 → S2)
 * 2) John left the house (S2 → S1)