%% syntaxe : n p Cnp
/Cnp {
3 dict begin
   /p exch def
   /n exch def
   n p sub p le 
      {
         /p n p sub store
      } 
   if
   p 0 eq
   p n eq
   or
      {1}
      {
         /i 0 def
         1
         p {n i sub p i sub div mul /i i 1 add store} repeat
      }
   ifelse
end
} def