reserve a,a1,a2,v,v1,v2,x for object;
reserve V,A for set;
reserve m,n for Nat;
reserve S,S1,S2 for FinSequence;

theorem Th22:
  S1 IsNDRankSeq V,A & S2 IsNDRankSeq V,A implies S1 c= S2 or S2 c= S1
  proof
    assume S1 IsNDRankSeq V,A & S2 IsNDRankSeq V,A;
    then
A1: S1 = FNDSC(V,A) | dom S1 & S2 = FNDSC(V,A) | dom S2 by Th20;
    dom S1 c= dom S2 or dom S2 c= dom S1 by Th3;
    hence thesis by A1,RELAT_1:75;
  end;
