theorem Th79:
  [:P,Q:] c= Indices M implies the_rank_of M >= the_rank_of Segm(M ,P,Q)
proof
A1: rng Sgm P=P by FINSEQ_1:def 14;
A2: rng Sgm Q=Q by FINSEQ_1:def 14;
  assume [:P,Q:] c= Indices M;
  hence thesis by A1,A2,Th78;
end;
