From the docs:
Predicate function negation: when the argument of ! is a function, it returns a function which computes the boolean negation of f.
!iseven is a function that returns
true if the argument is not even. I think it would be useful to generalize this behavior for infix operators, like
≈, etc. Currently
!== has its own definition, but
!≈ is undefined. If
! worked automatically for infix comparison operators,
!≈ would work.