Fix facade set category initialisation

[vdelecroix]

Facade sets are used in many places but there are two small errors that prevent from using it everywhere...

The first error concerns multiple categories initialisation. Here is a minimal example

class A(Parent):
    def __init__(self):
        Parent.__init__(self, 
            category=((FiniteEnumeratedSets(),Monoids()),
            facade=True)

for which we get

sage: A()
Traceback (most recent call last):
...
AttributeError: 'tuple' object has no attribute 'is_subcategory'

The second problem concerns the behavior of .facade_for() which is better explained with a minimal example

class B(Parent):
    def __init__(self):
        Parent.__init__(self, category=Sets(), facade=True)

for which we get

sage: b = B()
sage: b.facade_for()
Traceback (most recent call last):
...
AttributeError: 'B_with_category' object has no attribute '_facade_for'

The ticket provides the (trivial) corrections for both problems and add two doctests.

[slabbe]

Note: you may use ReST syntax for citing trac ticket :

:trac:`12796`

[tscrim]

 The associated combinat-devel discussion.

[vdelecroix]

Replying to slabbe:

Note: you may use ReST syntax for citing trac ticket :

:trac:`12796`

That's now done.

[vdelecroix]

I modified the behavior of facade_for() in the way it was discussed on combinat-devel (see comment:3 of Travis).

[vdelecroix]

Replying to vdelecroix:

Replying to slabbe:

Note: you may use ReST syntax for citing trac ticket :

:trac:`12796`

That's now done.

Actually, I missed one and now it's done!

[tscrim]

Looks good to me now. Thanks Vincent.

Travis

[tscrim]

Was this merged in 5.7.rc0?

[jdemeyer]

No.