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;

theorem Th59:
  for a being positive expression of C, an_Adj C holds Non a = (non_op C)term a
proof
  let a be positive expression of C, an_Adj C;
  not ex a9 being expression of C, an_Adj C st a = (non_op C)term a9 by Def37;
  hence thesis by Def36;
end;
