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 Th10:
  FNDSC(V,A).2 = NDSS(V,A\/NDSS(V,A))
  proof
    FNDSC(V,A).(1+1) = NDSS(V,A\/FNDSC(V,A).1) by Def3;
    hence thesis by Th9;
  end;
