Dear Maude Abusers,

I've updated prelude.maude and Maude-2.2.tar.gz in yesterday's
alpha86d release to fix some problems pointed out by Joe Hendrix. The
binaries are unaffected. I've also deleted diophantine.maude which
shouldn't have been in this directory in the first place (thanks
Narciso).

The problems pointed out by Joe were found by his sufficient
completeness checker. The easy one is that

  op nil : -> HookList .

needs to be a ctor. The subtle one arises from a confusion between __
lists of Qids with identity nil (used for type and Qid lists) and _,_
lists of Qids with identity empty (used for term and parameter
lists). The fix is a little tricky.

Firstly EmptyQidList is abolished along with all definitions involving
it. Since TypeList is a subsort of QidList, the use of nil in
processing TypeLists is allowed by adding the declaration

  op nil : -> TypeList [ctor] .

We still need to allow empty to be used in the processing of parameter
lists. Unfortunately ParameterList and  GroundTermList are
incomparable. So we create a new sort EmptyCommaList to hold empty
(which used to live in GroundTermList) and make this sort be below
both GroundTermList and ParameterList. 

To preserve the preregularity and associativity of _,_ we need the
extra declaration:

  op _,_ : EmptyCommaList EmptyCommaList -> EmptyCommaList [ctor ditto] .

The change in prelude.maude feeds through to changes in the test suite
results and both are updated in the new Maude-2.2.tar.gz

Steven