[sv-ac] Annex F proposal for 1668 updated

All:

Please find the updated Annex F proposal for 1668 on 
mantis.

The major changes are:

1. Added recursive function admits_empty.  This addresses
   Dmitry's concern about forward references to empty matching.

2. Removed restriction that sequence with local variable 
   declaration assignment not match empty.  The general
   rewrite is

      (t v=e; r)

   goes to

      (t v; k(r) ((1,v=e) ##0 r) or (r intersect 1[*0]))

   If admits_empty(r) = 0, the rewrite may be simplified to

      (t v; k(r) (1,v=e) ##0 r)

   If admits_empty(r) = 1, the rewrite may be simplified to

      (t v; k(r) ((1,v=e) ##0 r) or 1[*0]))

3. Added a note on the case of push on a sequence that points
   to the place in Clause 16 that says the sequence cannot admit
   empty match.

4. Changed the result of push as in the discussion with Ed to 
   use "##0" instead of "|->".

I can't attach the proposal here, so please see mantis.

J.H.


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