The Change command performs a change of variables in the integrals involved in v.

The second parameter c is the transformation (or list of transformations or set of transformations) in the form x=f(u) (assuming x is the original variable and u is the new variable). Implicit transformations (g(x)=h(u)) can be given as long as it is possible to unambiguously rewrite it as an explicit transformation.

The third parameter y is required only if the number of new symbols in the transformation is not equal to the number of old variables in v.