F comb(arr, k)
   I k == 0
      R [[Int]()]

   [[Int]] result
   L(x) arr
      V i = L.index
      L(suffix) comb(arr[i+1..], k-1)
         result [+]= x [+] suffix

   R result

print(comb([0, 1, 2, 3, 4], 3))