Applies the formula P_{n} (x) = sum_{i = 0 } ^{n } product _{k not i} (x - x_{k}) over (x_{i} - x_{k}) . points is a list like ( (x1 y1) (x2 y2) ... (xn yn)). This is the simplest formula for an interpolation. But this is an unefficient method, due to: a) you must recompute the coefficients every time you evaluate the polynomial and b) you can't recalculate a higger degree polynomial with the previous one. But if you want only a simple interpolation formula, this is for you.