We have things that are connected together, and things which border each other. The orientation of the objects or spaces needs to be represented. We will use an orientation operator, with four connections, two of which represent directions – here are some of the directional adjectives (some are prepositions, so they are enclosed in lists to prevent acquiring the wrong part of speech):
We will use "contiguous" to mean that regions or objects abut.
Will the orientation always be fixed – what if positions reverse, or do we then use a relation? Should we have a logical control anyway?
For a simple case of two components of a duct which are adjacent to each other, we end up with
The logical control means only that it should be used when it is true, and in a simple
case it is a true existential constant.
The downstream end of one part of the small intestine is contiguous with the upstream part
of the next.
For the esophagointestinal tract
