Comment fast lucas algo

lucas.py

@@ -129,6 +129,8 @@ def LucasVn(n, p, q):
 
 
 def LucasFast(k, p, q, n):
+    """Faster Lucas algorithm, modulo a number
+    """
     if k < 0:
         raise ValueError("k must be a non-negative integer")
     if n < 1: