added check_ methods
added check_ methods

armandobs14/rdflib,RDFLib/rdflib,marma/rdflib,marma/rdflib,dbs/rdflib,RDFLib/rdflib,ssssam/rdflib,ssssam/rdflib,avorio/rdflib,armandobs14/rdflib,avorio/rdflib,armandobs14/rdflib,RDFLib/rdflib,ssssam/rdflib,yingerj/rdflib,RDFLib/rdflib,dbs/rdflib,yingerj/rdflib,armandobs14/rdflib,ssssam/rdflib,dbs/rdflib,dbs/rdflib,yingerj/rdflib,yingerj/rdflib,avorio/rdflib,avorio/rdflib,marma/rdflib,marma/rdflib