proposition: Lemma sqrrB1 x : (x - 1) ^+ 2 = x ^+ 2 - x *+ 2 + 1.
proof: Proof. by rewrite -sqrrN opprB addrC sqrrD1 sqrrN mulNrn. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)