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procedure main()
   A := [8,24,52,100,1020,1024,10000]
   every len := !A do {
      deck := [: 1 to len :]
      tmpd := copy(deck)
      cnt := 0
      while (cnt +:= 1, tmpd := shuffledeck(tmpd)) do
         if lequiv(deck,tmpd) then break
      write("For deck of size ",len," it takes ",cnt," perfect shuffles.")
      }
end

procedure shuffledeck(d)
   c1 := create !d[1+:*d/2]
   c2 := create !d[*d/2+1:0]
   d := []
   while (put(d,@c1),put(d,@c2))
   return d
end