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HOL.thy:
"@" is no longer introduced as a "binder" but has its own explicit
translation rule "@x.b" == "Eps(%x.b)". If x is a proper pattern, further
translation rules for abstractions with patterns take care of the rest. This
is very modular and avoids problems with "binders" such as "!" mentioned
below.
let now allows pttrn (let (x,y) = t in u) instead of just idt (let x = t in u)
Set.thy:
UN, INT, ALL, EX, etc all use "pttrn" instead of idt. Same change as for "@"
above, except that "@" was a "binder" originally.
Prod.thy:
Added new syntax for pttrn which allows arbitrarily nested tuples. Two
translation rules take care of %pttrn. Unfortunately they cannot be
reversed. Hence a little ML-code is used as well.
Note that now "! (x,y). ..." is syntactically valid but leads to a
translation error. This is because "!" is introduced as a "binder" which
means that its translation into lambda-terms is not done by a rewrite rule
(aka macro) but by some fixed ML-code which comes after the rewriting stage
and does not know how to handle patterns. This looks like a minor blemish
since patterns in unbounded quantifiers are not that useful (well, except
maybe in unique existence ...). Ideally, there should be two syntactic
categories:
idts, as we know and love it, which does not admit patterns.
patterns, which is what idts has become now.
There is one more point where patterns are now allowed but don't make sense:
{e | idts . P}
where idts is the list of local variables.
Univ.thy: converted the defs for <++> and <**> into pattern form. It worked
perfectly.

I have modified the grammar for idts (sequences of identifiers with optional
type annotations). idts are generally used as in abstractions, be it
lambda-abstraction or quantifiers. It now has roughly the form
idts = pttrn*
pttrn = idt
where pttrn is a new nonterminal (type) not used anywhere else.
This means that the Pure syntax for idts is in fact unchanged.
The point is that the new nontermianl pttrn allows later extensions of this
syntax. (See, for example, HOL/Prod.thy).
The name idts is not quite accurate any longer and may become downright
confusing once pttrn has been extended. Something should be done about this,
in particular wrt to the manual.

Simplified proofs thanks to addss.