clojure - Understanding core.logic != -

i expect following expression return number of results, each of consists of 2 cons cells, 2 cons cells not equivalent. however, returns 0 results. why getting no results?

(run* [c1 c2]    (fresh [lx ly x1 y1 x2 y2]      (== lx [1 2])     (== ly [4 5])     (membero x1 lx)     (membero x2 lx)      (membero y1 ly)     (membero y2 ly)     (conso x1 y1 c1)     (conso x2 y2 c2)     (!= c1 c2))) 

examples of expected results:

• [(1 . 4) (2 . 5)]
• [(1 . 4) (1 . 5)]
• [(2 . 4) (2 . 5)]

i not expect return result [(1 . 4) (1 . 4)] both spots in each cons equal.

if remove (!= c1 c2) portion, 16 results, including both cons same.

i results expect if replace (!= c1 c2) with:

(conde   ((!= x1 x2))   ((!= y1 y2))) 

which should same thing, explicitly checks 2 cells.

this not valid core.logic program. cannot use conso tail not proper. minikanren in scheme let this, behavior undefined core.logic. i've amended docstring conso reflect this. working program:

(run* [c1 c2]    (fresh [lx ly x1 y1 x2 y2]      (== lx [1 2])     (== ly [4 5])     (membero x1 lx)     (membero x2 lx)      (membero y1 ly)     (membero y2 ly)     (== [x1 y1] c1)     (== [x2 y2] c2)     (!= c1 c2)))