Tacit Fibonacci and Factorial

   ($:@−&2+$:@<:)`[@.(<&2) "0 i.25
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368

   (*$:@<:)`1:@.(=&0) "0 i.15
1 1 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600 6227020800 87178291200
   (*$:@<:)^:(1&<) "0 i.15  NB. 0! is wrong
0 1 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600 6227020800 87178291200
   1:`(*$:@<:)@.* "0 i.15  NB. the shortest definition of factorial -- 14 chars
1 1 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600 6227020800 87178291200