Formal definition of `GeoRegion` that allows inferring an instance into the class

[rjyounes]

May not be possible in all cases. See parent issue for more discussion.

[philblackwood]

Might not resolve the issue stated, but ...

Adding (inverse(isGeoContainedIn) some GeoPoint) to the class equivalence statement would make it consistent with the way GeoVolume is defined.