Function DURATION-VALUE

The value of a duration, without a specified time line. We also support an existence assumption: an entity has existence only during its duration value.
Arity: 2
Range: Number
Subrelation-Of: Numeric-value
Axioms:
(=> (Duration-Value ?A ?B)
    (And (Exists (?Z ?T)
                 (And (Present ?T)
                      (Time-Span ?Z)
                      (Begins-At ?T ?Z)
                      (Exists (?C)
                              (And (Duration-Value ?Z ?C)
                                   (Identity ?C ?B)))
                      (Begins-At ?T (HAS-EXISTENCE ?A TRUE))
                      (Forall (?W ?T1)
                              (=> (And (Present ?T1)
                                       (/= ?T ?T1)
                                       (Time-Span ?W)
                                       (Begins-At ?T1 ?W)
                                       (Or (Precedes ?W ?Z)
                                           (Follows ?W ?Z)))
                                  (Exists (?E)
                                          (And (Not (Has-Existence 
                                                        ?A
                                                        True))
                                               (Begins-At ?T1 ?E)))))))
         (Exists (?U)
                 (And (Time-Unit ?U)
                      (Exists (?F)
                              (And (The-Time-Unit ?A ?F)
                                   (Identity ?F ?U)))))))