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
  S1 IsNDRankSeq V,A & S2 IsNDRankSeq V,A implies S1+*S2 IsNDRankSeq V,A
  by Th23;
