REWR_CONV_A : (thm -> conv)
[0 < n] |- (a * n = b * (n : int)) <=> (a = b)
f (a * m = b * (m : int)) x
[0 < m] |- f (a * m = b * m) x <=> f (a = b) x
f (a = b) x 0 < m