proposition: Lemma path_pcons x pi : e x (pi 0) -> path pi -> path (pcons x pi).
proof: Proof. move => H1 H2 [|k] //. exact: H2. Qed.
imports: mathcomp.ssreflect.ssreflect mathcomp(all_ssreflect) CompDecModal.libs(edone bcase fset base modular_hilbert sltype)