PrintCouplings() of Coupled to check the coupling
status. The couplings of the ping-pong game are displayed as
follows.
Inside of PingPong -- External Input Coupling (EIC) -- ------ # of EICs: 0----- -- Internal Coupling (ITC) -- A.send --> B.receive B.send --> A.receive ------ # of ITCs: 2----- -- External Output Coupling (EOC) -- ------ # of EOCs: 0-----