apple-0.1.0.0: math/erf.apple

-- https://mathworld.wolfram.com/Erf.html
λz.
{
  ffact ← [(*)/ₒ 1 (𝒻 1 x (⌊x))];
  Σ ← λN.λa. (+)/ₒ 0 (a'(⍳ 0 N 1));
  (2%√𝜋)*Σ 30 (λn. {nf⟜ℝn; ((_1^n)*z^(2*n+1))%((ffact nf)*(2*nf+1))})
}