fact: Definition addf x y : dom := Ratio (\n_x * \d_y + \n_y * \d_x) (\d_x * \d_y).
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)