From I remember from what we did in maths, a liar is usually used to have a NOT ...

yashasolutions 18 days ago | parent | context | favorite | on: A liar who always lies says "All my hats are green...

From I remember from what we did in maths, a liar is usually used to have a NOT so we have something like NOT (All my hats are green) => There is at least one hat that is not green.