⍝ Perfect Ripple Shuffle:

    show←⊃¨∘⊂∘(,'HCDS'∘.,'A23456789XJQK')               ⍝ show card(s) no. ⍵.

    ⍝ Hearts, Clubs, Diamonds, Spades.
    ⍝ ¯       ¯      ¯         ¯
    ⍝ Ace 2-9 X(10) Jack Queen King.
    ⍝ ¯       ¯     ¯    ¯     ¯

    ⍕show 4 13⍴⍳52                                      ⍝ show deck in order
 HA  H2  H3  H4  H5  H6  H7  H8  H9  HX  HJ  HQ  HK 
 CA  C2  C3  C4  C5  C6  C7  C8  C9  CX  CJ  CQ  CK 
 DA  D2  D3  D4  D5  D6  D7  D8  D9  DX  DJ  DQ  DK 
 SA  S2  S3  S4  S5  S6  S7  S8  S9  SX  SJ  SQ  SK 

    ⍕show 4 13⍴ ripple ⍳52                              ⍝ shuffled deck
 DA  HA  D2  H2  D3  H3  D4  H4  D5  H5  D6  H6  D7 
 H7  D8  H8  D9  H9  DX  HX  DJ  HJ  DQ  HQ  DK  HK 
 SA  CA  S2  C2  S3  C3  S4  C4  S5  C5  S6  C6  S7 
 C7  S8  C8  S9  C9  SX  CX  SJ  CJ  SQ  CQ  SK  CK 

    ripple ⍳16                              ⍝ 1-8 interleaved with 9-16
9 1 10 2 11 3 12 4 13 5 14 6 15 7 16 8

    ripple ripple ⍳16                       ⍝ double shuffle.
13 9 5 1 14 10 6 2 15 11 7 3 16 12 8 4

    3 ripple pow ⍳16                        ⍝ triple shuffle.
15 13 11 9 7 5 3 1 16 14 12 10 8 6 4 2

    4 ripple pow ⍳16                        ⍝ (÷∘4⍴⍵)-shuffle reverses.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

    8 ripple pow ⍳16                        ⍝ (÷∘2⍴⍵)-shuffle restores.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

⍝∇ ripple pow

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