n          n!         n-i  i
t B (t)= t ──────── (1-t)    t                                    
   i       (n-i)!i!
         i+1        (n+1)!             (n+1)-(i+1)  i+1
       = ─── ──────────────────── (1-t)            t              
         n+1 ((n+1)-(i+1))!(i+1)!                                 
         i+1        k!             k-(i+1)  i+1
       = ─── ──────────────── (1-t)        t   ,  where  k = n + 1
          k  (k-(i+1))!(i+1)!
         i+1  k
       = ─── B   (t)                                              
          k   i+1