message: Write `not(a)` as `!a`
diff: @@ -205,6 +205,8 @@ fn write_expr<W: io::Write>(
  E::Call(ref call) => {
  if &**call.name == "norm" && call.args.len() == 1 {
  write_norm(w, rt, &call.args[0], tabs)?
  + } else if &**call.name == "not" && call.args.len() == 1 {
  + write_not(w, rt, &call.args[0], tabs)?
  } else {
  write_call(w, rt, call, tabs)?
  }
  @@ -423,6 +425,16 @@ fn write_binop<W: io::Write>(
  Ok(())
  }
  +fn write_not<W: io::Write>(
  + w: &mut W,
  + rt: &Runtime,
  + expr: &ast::Expression,
  + tabs: u32,
  +) -> Result<(), io::Error> {
  + write!(w, "!")?;
  + write_expr(w, rt, &expr, tabs)
  +}
  +
  fn write_unop<W: io::Write>(
  w: &mut W,
  rt: &Runtime,
  