e' includes e as a nonfinal part: e is part of e', and the run time of e is a
nonfinal subinterval of that of e'.
- NonfinalPart e e' = (e ≤ e' ∧ (Event.τ e).NonfinalSubinterval (Event.τ e'))
Used by InProgress, inProgress_iff, NonfinalPart.lt, InProgress.exists_of_isTotallyRealistic
Used in Portner1998