theorem Th40:
  for k being Nat holds k+1 in SUCC(k,SCM+FSA) &
   for j being Nat st j in SUCC(k,SCM+FSA) holds k <= j
proof
  let k be Nat;
A1: SUCC(k,SCM+FSA) = {k, k+1} by Th39;
  hence k+1 in SUCC(k,SCM+FSA) by TARSKI:def 2;
  let j be Nat;
  assume
A2: j in SUCC(k,SCM+FSA);
  per cases by A1,A2,TARSKI:def 2;
  suppose
    j = k;
    hence thesis;
  end;
  suppose
    j = k + 1;
    hence thesis by NAT_1:11;
  end;
end;
