Why no RE match of A AND B?

[Anders J. Munch]

"Tim Peters" <tim.one at comcast.net> wrote:
> [Anders J. Munch]
> > It's [regexp intersection] useful in combination with complement ("it's
> > a .*day but not a Sunday").
> 
> If that's the use case, it's more an argument for adding a difference
> operator (like R-S = the strings matched by R less the strings matched by
> S).

That might be so.  Not that I'm proposing to add anything of either
kind.

It's easier though to express difference through intersection and
complement
  R-S = R & ~S
than the other way around
  R & S = (R|S) - (R-S) - (S-R)

- Anders