proposition: Lemma ger1_psum x : summable S -> `|S x| <= psum S.
proof: Proof. move=> smS; have h := @ger_big_psum [:: x] _ smS. by rewrite (le_trans _ (h _)) ?big_seq1. Qed.
imports: mathcomp(all_ssreflect all_algebra) mathcomp.classical(boolp) xfinmap ereal reals discrete realseq mathcomp.classical(classical_sets functions mathcomp_extra) topology