DURATION denotes a period of time. It consists of a value and a measure
(=> (Time-Range.Duration $X $Y) (Duration $Y)) (=> (Time-Point.Unit $X $Y) (Duration $Y)) (Nth-Domain Tp+ 2 Duration) (=> (Duration.Value $X $Y) (Duration $X)) (=> (Duration.Measure $X $Y) (Duration $X)) (=> (Dr= $X $Y) (Duration $Y)) (=> (Dr= $X $Y) (Duration $X)) (=> (Dr< $X $Y) (Duration $Y)) (=> (Dr< $X $Y) (Duration $X)) (Nth-Domain Dr+ 3 Duration) (Nth-Domain Dr+ 2 Duration) (Nth-Domain Dr+ 1 Duration)