Proof;Only Reciprocal Circuit are passive circuit

Consider a two-port reciprocal network :

$$\ Y= \left[ {\begin{array}{cc} 0 & -1/2 \\ -1/2 & 0 \\ \end{array} } \right] \ $$
then how can we proof that it is a passive network or circuit?

I have no idea how to prove it ....any hints or suggestions please...?

Answer

Prove that the circuit only dissipates energy, never creates it. (=the total input power via the ports to the circuit must be greater or equal to zero), no matter what thevenin sources are connected to it.