reserve A for preIfWhileAlgebra,
  C,I,J for Element of A;
reserve S for non empty set,
  T for Subset of S,
  s for Element of S;

theorem Th55:
  for A being partial non-empty non empty UAStr st A is ECIW-strict
  for o being OperSymbol of A holds o = 1 or o = 2 or o = 3 or o = 4
proof
  let A be partial non-empty non empty UAStr;
  assume signature A = ECIW-signature;
  then 4 = len the charact of A by Th54,UNIALG_1:def 4;
  then dom the charact of A = Seg 4 by FINSEQ_1:def 3;
  hence thesis by ENUMSET1:def 2,FINSEQ_3:2;
end;
