Equivalence of expressions up to permutation of variables

Is there an existing Maxima function which will establish a possible 
substitution of variables [v_i=u_i,... with the property that

subst(v_i=u_i,...,ex_1)=ex_2

The function should return the permutaion as a list of equations, or 
false.

There are different notions of "equality" here including
  (1) that above, based on Maxima's data structure and
  (2) ratsimp(subst(v_i=u_i,...,ex_1)-ex_2)=0.

Any suggestions welcome, particularly any which do not rely on an 
exhaustive search of the permutations of "n" variables!

Thanks
Chris