reserve i for Nat,
  j for Element of NAT,
  X,Y,x,y,z for set;
reserve C for initialized ConstructorSignature,
  s for SortSymbol of C,
  o for OperSymbol of C,
  c for constructor OperSymbol of C;
reserve a,b for expression of C, an_Adj C;
reserve t, t1,t2 for expression of C, a_Type C;
reserve p for FinSequence of QuasiTerms C;
reserve e for expression of C;
reserve a,a9 for expression of C, an_Adj C;
reserve q for pure expression of C, a_Type C,
  A for finite Subset of QuasiAdjs C;
reserve T for quasi-type of C;

theorem
  for T being quasi-type of C for a being quasi-adjective of C holds
  vars (a ast T) = (vars a) \/ (vars T)
proof
  let T be quasi-type of C;
  let a be quasi-adjective of C;
  thus vars (a ast T) = varcl((variables_in a)\/variables_in T) by Th102
    .= (vars a) \/ vars T by Th11;
end;
