The 1999 Siggraph torus implementation at https://www.siggraph.org/education/materials/HyperGraph/mapping/torustx.htm
lists uv coords as:
v = arccos (Y/R)/2p
u = [arccos ((X/(R + r*cos(2 pv))]2p
What’s up with the u expression syntax (unbalanced parentheses); is it a typo or denoting/implying something else?
(since it was presented at Siggraph 15 yrs ago I imagine someone would have caught the typo by now