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 Th9:
  FNDSC(V,A).1 = NDSS(V,A)
  proof
    FNDSC(V,A).(0+1) = NDSS(V,A \/ FNDSC(V,A).0) & FNDSC(V,A).0 = A by Def3;
    hence thesis;
  end;
