clojure/core.logic — pull request #9 by abrooks (2012-09-02 01:17:22+00:00)
Title: LOGIC-50: Rel relation PersistentHashSet becomes LazySeq after issuing a retraction

This issue does not affect external correctness but will adversely
affect performance in the presence of duplicated facts.

http://dev.clojure.org/jira/browse/LOGIC-50