real procedure La(n, X);
   comment This procedure computes the Laguerre polynomial
     Ln(X) = exp(X) * (d^n/dX^n(exp(-X)) 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 ≔ 1 - 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 ≔ (1 + 2 × i - X) × b - (i⭡2) × a;
         a ≔ b;
         b ≔ c
      end;
   La ≔ c
end;