Unproductive result displayed

[flexoron]

v0.9.4-135-g7cfe8ee5

?- X = [+, Z-Z, Z-Z+Z], Z = Z-Z+Z, Z =.. X.
   X = [+,Z-Z+Z-(Z-Z+Z),Z-Z+Z-(Z-Z+Z)+(Z-Z+Z)], Z = Z-Z+Z.

?-     [+,Z-Z+Z-(Z-Z+Z),Z-Z+Z-(Z-Z+Z)+(Z-Z+Z)] = [+, Z-Z, Z-Z+Z].
   Z = Z-Z+Z. % Z retrievable

?- Z = Z-Z+Z, Z =.. X, X = [+, Z-Z, Z-Z+Z].
   Z = Z-Z+Z, X = [+,Z+(Z-Z+Z)-(Z-Z+Z-(Z-Z+Z)),Z-Z+Z].

?-                [+,Z+(Z-Z+Z)-(Z-Z+Z-(Z-Z+Z)),Z-Z+Z] = [+, Z-Z, Z-Z+Z].
   false. % Z not retrievable