Nice node Mike.

I took a very brief look, and see symmetry in the code, for the a,b,c,d, so have no idea.
Will look longer tonight, if someone else does not figure it out first.
The a, b, c, d have to be sequentially added in to the node... (?)

- Brian

By the way, The Pringle reconstituted potato chip has the hyperbolic paraboloid shape, with some sort of rounding.
No Pringle measurements were made, just stuck in 1.618 as a "golden" ratio, as a guess. (Some talk on Alibre forum.)
(Trim can be done with circle, ellipse, etc.)
(The polylines are linear.)