Containers and membership subject/object asymmetry

I'm experiencing mild anxiety about containers and membership
subject/object asymmetry. Consider the Steve's friends example.



Consider an LDPR representing Steve foaf profile <http://example.org/steves
>:



<> a ldp:Resource, foaf:PersonalProfileDocument ;

                foaf:primaryTopic <#me> .



<#me> a foaf:Person ;

                foaf:name "Steve" ;

                foaf:nick "SteveS" .



And another LDPR representing Richard's foaf profile <
http://example.org/cygri>:



<> a ldp:Resource, foaf:PersonalProfileDocument ;

                foaf:primaryTopic <#me> .



<#me> a foaf:Person ;

                foaf:name "Richard" ;

                foaf:nick "cygri" .



To represent Steve's friends, I'll create a container <
http://example.org/steves/friends>. Note that the membership subject is not
the container, nor the LDPR for SteveS, but the hash URI representing Steve
himself, because the subject of the 'knows' predicate is a Person rather
than a document. Now I want to assert that Steve knows Richard as defined
below. Note that the object of 'knows' is also a Person.



<> a ldp:Container ;

                ldp:membershipSubject foaf:knows ;

                ldp:membershipSubject <http://example.org/steves#me> .



<http://example.org/steves#me> foaf:knows <http://example.org/richard#me> .



Here comes the asymmetry; while I can use a hash URI as the membership
subject, I can't see how I can construct the above reference to the member
hash URI < http://example.org/richard#me> using POST. Could we allow a URL
to be POSTed (with an empty body) to a container via Content-Location? Is
this perhaps something along the lines that Roger Menday was asking for
(atomic operations)?



Thoughts?



Steve.