fact: Definition phi_rec f (x: T3) := if x is cons a b c n d then if (d==zero) then if n is n.+1 then phi1 (cons a b c n zero) (phi_rec_psi f a b c) else phi_rec_psi f a b c else phi1 (cons a b c n zero) (f d) else phi0.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)