proposition: Lemma prl_r2_sf_prop1: projective_system_on prl_r2_sf (cst_graph (psI S) F) (psI S) (psr S) (cst_graph (psr S) (identity F)).
proof: Proof. apply:prl_exa2_prop. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)