reserve k,m,n for Element of NAT,
  a,X,Y for set,
  D,D1,D2 for non empty set;
reserve p,q for FinSequence of NAT;
reserve x,y,z,t for Variable;
reserve F,F1,G,G1,H,H1 for ZF-formula;
reserve sq,sq9 for FinSequence;

theorem
  H is universal implies (x = bound_in H iff ex H1 st All(x,H1) = H) & (
  H1 = the_scope_of H iff ex x st All(x,H1) = H) by Def33,Def34;
