I'm trying to make a substitute for Tristan Jehan's
mapper object, pending it's porting (I hope) to UB.
What I have below works as far as it goes, but I would
like it to generate a wider variety of curves, like
mapper does. In particular, I want to be able to
generate the 'inverse' of the curve. I guess it's a
job for expr, but the maths is failing me.
( I imagine there is a Litter object that does exactly
this, but as the UB versions are not yet available for
non-pro users, I'll have to be patient ;-)