I want to input an equation, to be solved later in combination with many other equations, that reads f(q,t) == g(1/t, 1/q), where f and g are some functions of q and tt to be determined precisely by the other equations.  The problem is, I don't know how to input this equation: if I just use variables f and g and then write something like f/.{t->q, q->t} == g, then the replacement rule evaluates immediately and the equation to be solved becomes f==g, which is not what I want.  How should I input this equation into Mathematica?  Sorry if this question is obvious--I'm a Mathematica novice.