x has a neighborhood y when x is part of the interior of y, which is part of any interior x is part of. This function is not very useful without an account of regions, which states the fundamental ontological distincion between objects and regions where objects are localized. See also theory:positions.
(=> (Neighborhood ?A ?B)
(And (Exists (?C) (And (Interior ?B ?C) (Part-Of ?A ?C)))
(Forall (?Z)
(=> (Exists (?D)
(And (Interior ?Z ?D) (Part-Of ?A ?D)))
(Part-Of ?B ?Z)))))