13.20 - Principle of Reciprocity - as a decreases b increases simultaneously and vice versa. Syntropic and Entropic wave phases are reciprocal. 1) Mutual, correlative, correspondent, complementary. 2) Moving alternately backward and forward. 3) Mutually responsive, answering. 4) Inversely or responding, inverse. 5) A thing that is reciprocal to something else; a return, an equivalent; a counterpart; a complement; that which a given quantity is multiplied to produce Unity.