examples: ``` sqlite> select 2 is true; -- boolean literal changes the meaning 1 sqlite> select 2 is +true; -- back to "2 is 1" 0 sqlite> select 2 is (1==0); -- also "2 is 1" 0 sqlite> select 2 is (true); -- redundant parens don't spoil it 1 sqlite> select null is true <= true; -- not a unitary operator 0 ```