reserve i,j for Nat;

theorem
 for C being initialized standardized ConstructorSignature
 for e being expression of C
  holds not (e.{})`1 in Vars iff (e.{})`1 is OperSymbol of C
  proof let C be initialized standardized ConstructorSignature;
   let e be expression of C;
A1:  (e.{})`1 in Vars or (e.{})`1 in the carrier' of C or
     (e.{})`1 = ast C or (e.{})`1 = non_op C by Th14;
     Vars misses the carrier' of C by Th10;
    hence not (e.{})`1 in Vars iff (e.{})`1 is OperSymbol of C
     by A1,XBOOLE_0:3;
  end;
