Dear All, I am trying to translate some codes of mine into haskell. It looks like Haskell can shorten quite a bit the implementation of mathematical formulas. Let us say you have two list of real numbers; let us call them y and t. The list t is increasing (a sort of time). Now consider the couples (t_a, y_a) and (t_b,y_b) where t_a<t_b i.e. two (non-simultaneous) values of t and the corresponding y_a and y_b. There are no assumptions on y. What I would like to write is a function which checks the existence (t_c,y_c), where y_a<y_c<y_b (i.e. y_c is some intermediate time) such that y_c<y_b+(y_a-y_b)*(t_b-t_c)/(t_b-t_a). I have already implemented this in other languages, but I ended up with quite lengthy functions (what if a list is empty, what if it has fewer than 2-3 elements and so on...). Also, it would be nice to iterate this function on all possible combinations (t_a, y_a) and (t_b,y_b), t_a<t_b I can form from my data. I am not asking someone to 'do my homework', rather I would like to see how much more compact things can get in haskell. Many thanks Lorenzo