λxs.λys.
{
  Σ ← [(+)/x];
  n ⟜ ℝ(:xs);
  xbar ⟜ (Σ xs) % n; ybar ⟜ (Σ ys) % n;
  xy ⟜ Σ ((*)`xs ys);
  x2 ⟜ Σ ((^2)'xs);
  denom ⟜ (x2-n*(xbar^2));
  a ← ((ybar*x2)-(xbar*xy))%denom;
  b ← (xy-(n*xbar*ybar))%denom;
  (a,b)
}