Which sport includes Popular formations include the 4-2 , 6-2 , and 5-1 systems ?
4 → 3 → 2 = 4 → ( 4 → (4) → 1 ) → 1 ( by 4 ) and then , working from the inner parentheses outwards , = 4 → ( 4 → 4 → 1 ) → 1 ( remove redundant parentheses ) = 4 → ( 4 → 4 ) → 1 (3) = 4 → ( 256 ) → 1 (2) = 4 → 256 → 1 ( rrp ) = 4 → 256 (3) = 4256 (2) = 13 407 807 929 942 597 099 574 024 998 205 846 127 479 365 820 592 393 377 723 561 443 721 764 030 073 546 976 801 874 298 166 903 427 690 031 858 186 486 050 853 753 882 811 946 569 946 433 649 006 084 096 exactly ≈ 1.34078079299 × 10154 With Knuth 's arrows : formula_192 → 2 → 4 = 2 → (2) → 3 ( by 4 ) = 2 → 2 → 3 ( rrp ) = 2 → 2 → 2 ( 4 , rrp ) = 2 → 2 → 1 ( 4 , rrp ) = 2 → 2 (3) = 4 (2) ( In fact any chain beginning with two 2s stands for 4. )