real procedure He(n, X);
   comment This procedure computes the Hermite polynomial
     Hn(X) = (-1)^n * exp(X^2) * (d^n/dX^n(exp(-X^2)) for any
     given real argument X, and any order, n, by
     the recursion formula below;
   integer n;
     real X;
begin
   real a, b, c;
   integer i;
   a ≔ 1;
   b ≔ 2×X;
   if n = 0 then c ≔ a else if n = 1 then
     c ≔ b else for i ≔ 1 step 1 until n - 1 do
      begin
         c ≔ 2 × X × b - 2 × i × a;
         a ≔ b;
         b ≔ c
      end;
   He ≔ c
end;