:OR

Purpose

Creates a disjunctive reasoning branch that succeeds if either branch succeeds.

  (:OR ((Color MyHouse Green)  (Color NeighborsHouse Yellow))
       ((Color myHouse Yellow) (Color NeighborsHouse Green)))

Succeeds if any of the given paths succeed.

Fails if all of the given paths fail.

Only one path succeeds, so only one binding set is returned. This means that you can use the same variable names in both paths without fear of conflict. Each path is run in an independent subroutine.
Side effects from partially-executed paths will not be removed from the KB if the path fails.