labelOrTail: (uri) ->

    try

      @graph.stringValue(uri, @graph.Uri('rdfs:label'))

    catch

      words = uri.split('/')

      words[words.length-1]

  objects: (s, p) ->

    @_autoDeps.askedFor(s, p, null, null)

    quads = @graph.findByIRI(s, p)

    return (q.object for q in quads)

  subjects: (p, o) ->

    @_autoDeps.askedFor(null, p, o, null)

    quads = @graph.findByIRI(null, p, o)

    return (q.subject for q in quads)

  items: (list) ->

    out = []

    current = list

    while true

      if current == RDF + 'nil'

        break

      firsts = @graph.findByIRI(current, RDF + 'first', null)

      rests = @graph.findByIRI(current, RDF + 'rest', null)

      if firsts.length != 1

        throw new Error("list node #{current} has #{firsts.length} rdf:first edges")

      out.push(firsts[0].object)

      if rests.length != 1

        throw new Error("list node #{current} has #{rests.length} rdf:rest edges")

      current = rests[0].object

    return out

  contains: (s, p, o) ->

    @_autoDeps.askedFor(s, p, o, null)

    return @graph.findByIRI(s, p, o).length > 0

  nextNumberedResources: (base, howMany) ->

    results = []

    # we could cache [base,lastSerial]

    for serial in [0..1000]

      uri = @Uri("#{base}#{serial}")

      if not @contains(uri, null, null)

        results.push(uri)

        if results.length >= howMany

          return results

    throw new Error("can't make sequential uri with base #{base}")

  nextNumberedResource: (base) ->

    @nextNumberedResources(base, 1)[0]       

  contextsWithPattern: (s, p, o) ->

    ctxs = []

    for q in @graph.find(s, p, o)

      ctxs.push(q.graph)

    return _.unique(ctxs)