Functor brackets

[Andrzej Trybulec <trybulec@math.uwb.edu.pl>]

Czeslaw Bylinski implemented new rules for functor brackets. We used to
have them paired, i.e. left and right functor brackets were counted in
vocabularies and in a term closing (right) functor bracket must have the
same number as the left one; if not, a syntactic error was reported.

One may introduced now formats, in which functors brackets are not
paired.

In  MEASURE5 Jozef Bialas has introduced the following formats:
[.a,b.] - for an interval closed on both sides
].a,b.[ - for an interval open on both sides
(.a,b.> - for an interval open on the left side (and closed on the
right)
<.a,b.) - for an interval open on the right side (and closed on the
left)
(MEASURE:def 1,def 2, def 3, def 4)

It is for extended reals, the same may be useful for reals, lattices,
posets.

Because of new rules it might be simplified to

[.a,b.]
].a,b.[
].a,b.]
[.a,b.[

It seems more readable and easier to remember.
I guess the Library Committee will revise MEASURE5.

Any comment?

Andrzej Trybulec