A difference between tow time points ?tp1 and ?tp2 is aduration ?duration.
(Nth-Domain Tp+ 3 Time-Point) (Nth-Domain Tp+ 2 Duration) (Nth-Domain Tp+ 1 Time-Point)
(Tp= (Tp+ (Time-Range.Start-Time ?Time-Range) (Time-Range.Duration ?Time-Range)) (Time-Range.End-Time ?Time-Range)) (=> (Time-Range ?Time-Range) (Tp= (Tp+ (Time-Range.Start-Time ?Time-Range) (Time-Range.Duration ?Time-Range)) (Time-Range.End-Time ?Time-Range))) (=> (= (Tr+ ?Tr1 ?Duration) ?Tr2) (= (Tp+ (Time-Range.End-Time ?Tr1) ?Duration) (Time-Range.End-Time ?Tr2)))