On Monday, January 5, 2015 at 12:37:44 PM UTC-8, xorxes wrote:
I'm not sure what the advantage would be of having a separate word
One advantage would be clarity.
In my life, vertical is a simple observational approximation.
Vertical things are approximately parallel with a standing human,
or plumb line.
x1 seems vertical (straight up and down) to observer x2
If an infinite line and infinite plane are conceptual objects,
then two of them forming all equal angles is a unique conceptual relationship.
Applying gravity seems forced to me.
Based on your examples it seems like we only need two places:
x1 forms all equal angles (is perpendicular) with x2
I would probably create another word for:
x1 forms a 90 degree angle with x2