minor: code indent fix
FIXED: remove hack to only return materialized mappings
exploit new Options parameter of concept_results to pass strategy to check concept mappings from non-materialized graphs
pass strategy when fetching concepts
added correspondence_element/3 convenience predicate
ADDED: is_mapped/4 checks if concept has been mapped, even if mapping has not been materialized
check mappings for non-materialized graphs
IMPROVED: do not need to materialize every final mapping