  In two-qubit gate simulations an entangling gate is used several times
together with single qubit gates to simulate another two-qubit gate. We show
how a two-qubit gate's simulation power is related to the simulation power of
its mirror gate. And we show that an arbitrary two-qubit gate can be simulated
by three applications of a super controlled gate together with single qubit
gates. We also give the gates set that can be simulated by n applications of a
controlled gate in a constructive way. In addition we give some gates which can
be used four times to simulate an arbitrary two-qubit gate.
