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
  <*NDSS(V,A),NDSS(V,A\/NDSS(V,A)),NDSS(V,A\/NDSS(V,A\/NDSS(V,A)))*>
   IsNDRankSeq V,A
  proof
    set S = <*NDSS(V,A),NDSS(V,A\/NDSS(V,A))*>;
    len S = 2 & S.2 = NDSS(V,A\/NDSS(V,A)) by FINSEQ_1:44;
    hence thesis by Th17,Th28;
  end;
