to the greatest distance in space or time (`farthest' is used more often than `furthest' in this physical sense); "see who could jump the farthest"; "chose the farthest seat from the door"; "he swam the furthest"
necessarily or demonstrably true; "demonstrable truths"
capable of being demonstrated or proved; "obvious lies"; "a demonstrable lack of concern for the general welfare"; "practical truth provable to all men"- Walter Bagehot