ISSUE-75: non-monotonic ldp:membershipXXX relations

More formally:

In the "RDF Semantics" spec there is a section entitled
"Monotonicity of semantic extensions"
http://www.w3.org/TR/rdf-mt/#entail

Subgraph Lemma. A graph entails all its subgraphs.

example1: ldp:membershipPredicate
---------------------------------

So
{ <> a ldp:Container;
ldp:membershipPredicate ex:attachment . }
entails
{ <> a ldp:Container }

so what does entailment mean?

[[
Entailment is the key idea which connects model-theoretic semantics to real-world applications. As noted earlier, making an assertion amounts to claiming that the world is an interpretation which assigns the value true to the assertion. If A entails B, then any interpretation that makes A true also makes B true, so that an assertion of A already contains the same "meaning" as an assertion of B; one could say that the meaning of B is somehow contained in, or subsumed by, that of A. If A and B entail each other, then they both "mean" the same thing, in the sense that asserting either of them makes the same claim about the world. The interest of this observation arises most vividly when A and B are different expressions, since then the relation of entailment is exactly the appropriate semantic license to justify an application inferring or generating one of them from the other. Through the notions of satisfaction, entailment and validity, formal semantics gives a rigorous definition to a notion of "meaning" that can be related directly to computable methods of determining whether or not meaning is preserved by some transformation on a representation of knowledge.
]]

but according to the current spec the world where

{ <> a ldp:Container .}

is true is the world where

{ <> ldp:membershipPredicate rdf:member . }

And that world is I am told incompatible with the world where

{ <> ldp:membershipPredicate ex:attachment }

unless

{ ex:attachment rdfs:subPropertyOf rdfs:member . }

example 2: ldp:membershipSubject
--------------------------------

Let's take the more complex example

{ <> a ldp:Container;
ldp:membershipPredicate ex:attachment .
ldp:membershipSubject <../bugs/13> }

entails according to the Subgraph Lemma

{ <> a ldp:Container . }

but the world in which that entailment is true
is according to our spec the world where

{ <> a ldp:Container;
ldp:membershipPredicate rdfs:member .
ldp:membershipSubject <> } .

But according to our spec you can't have two distinc ldp:membershipSubjects.
Therfore

{ <> owl:sameAs <../bugs/13> }

Which I don't think is the intended consequence.

Closed, if membershipSubject, membershipPredicate, and membershipPredicateInverse remain in LDP, they MUST be expressed in every LDPC
See http://www.w3.org/2013/meeting/ldp/2013-06-18#resolution_7