Re: Meaning of the ill decoration (was: Motion 42: NO)
The primary purpose of the "ill" decoration is to permit interval
constructors to report that their (non-interval) arguments were
invalid, i.e. did not describe ANY interval, not even Empty.
This notion is relevant and should not be discarded.
I never liked the notion that functions should try to report whether
their domain was empty. It is not even an extrapolation from the
behaviour of constructors: all arguments of interval functions are
intervals except for NaI (i.e. Empty_ill), which explicitly denotes
not being an interval.
Michel.
---Sent: 2013-02-07 15:12:52 UTC