(rembero x l o)
A relation between l and o where x is removed from l exactly one time.
;;https://github.com/clojure/core.logic/blob/master/src/main/clojure/clojure/core/logic.clj#L2483
;; (rembero x l o)
;; my simple reminder is: x+o=l (L, not 1)
(run* [q]
(fresh [a b x y]
(== q [a b])
(rembero a [:apple :banana :carrot] x)
(rembero b x y)))
;; ([:apple :banana] [:apple :carrot] [:banana :apple] [:banana :carrot] [:carrot :apple] [:carrot :banana])