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 ;-) cheers Roger