theorem
  for a holds main-constr ((non_op MaxConstrSign)term a) = non_op
  proof set C = MaxConstrSign;
    set m = non_op C;
    let a;
A1: len the_arity_of m = 1 by Def14;
    the_arity_of m = <*an_Adj*> by ABCMIZ_1:38; then
    (the_arity_of m).1 = an_Adj C; then
A2: m term a = [m, the carrier of C]-tree <*a*> by A1,ABCMIZ_1:def 30;
    thus main-constr (m term a) = ((m term a).{})`1 by Def9
    .= [m, the carrier of C]`1 by A2,TREES_4:def 4
    .= non_op;
  end;
