reserve i,j for Nat;
reserve i,j for Nat,
  x for variable,
  l for quasi-loci;
reserve C for initialized ConstructorSignature,
  c for constructor OperSymbol of C;
reserve a,a9 for quasi-adjective,
  t,t1,t2 for quasi-term,
  T for quasi-type,

  c for Element of Constructors;

theorem Th42:
  for o being OperSymbol of MaxConstrSign holds
  o is constructor iff o in Constructors
  proof
    let o be OperSymbol of MaxConstrSign;
A1: the carrier' of MaxConstrSign = {*, non_op} \/ Constructors
    by ABCMIZ_1:def 24;
    o is constructor iff o nin {*,non_op} by TARSKI:def 2;
    hence thesis by A1,ABCMIZ_1:39,XBOOLE_0:3,def 3;
  end;
