(4) Adaptor: P1 +adap= P2 is the adaptor that inputs information from the environment and modifies elements of P1 to produce P2 according to the adaptation rule. Therefore the cardinality of P2 usually is the same as that of P1.

(5) Propagator: P1 =prop+ P2 is the propagator that outputs information to the environment and modifies elements of P1 to produce P2 according to the propagation rule. In the simplest case P2 is identical to P1. Therefore the cardinality of P2 usually is the same as that of P1.