theorem
  for L being add-associative right_zeroed right_complementable
        non empty addLoopStr
  for x,y being Element of L holds
  seq(n,x) - seq(n,y) = seq(n,x-y)
  proof
    let L be add-associative right_zeroed right_complementable
          non empty addLoopStr;
    let x,y be Element of L;
    thus seq(n,x) - seq(n,y) = seq(n,x) + seq(n,-y) by Th30
    .= seq(n,x-y) by Th29;
  end;
