
theorem LMExtBit6:
  for K be non zero Nat,
  x,y be Tuple of K, BOOLEAN
  st x, y are_summable
  & ( x . (len x) =1 or y . (len y) =1)
  holds
  (x + y) .len (x+y) =1
  proof
    let K be non zero Nat,
    x,y be Tuple of K, BOOLEAN;
    assume AS: x, y are_summable & ( x.(len x) =1 or y . (len y) =1);
    x+y =y+x by LMExtBit500;
    hence (x + y) .len (x+y) =1 by LMExtBit60,LMExtBit61,AS;
  end;
