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RE: Horse Race Puzzle (fwd)

  • To: mathgroup at
  • Subject: [mg9259] RE: [mg9162] Horse Race Puzzle (fwd)
  • From: Robert Pratt <rpratt at>
  • Date: Fri, 24 Oct 1997 01:01:14 -0400
  • Sender: owner-wri-mathgroup at

I omitted "{x," in the second replacement rule, which should read
"->{x,Flatten[{y,n}],z}}".  The corrected version appears below.  

> The solutions can be computed recursively using pattern matching as 
> follows:
> HorseRaces[1]={{1}};
> HorseRaces[n_]:=HorseRaces[n]=
> 	Join[
> Flatten[Map[ReplaceList[#,{x___,y___}->{x,n,y}]&,HorseRaces[n-1]],1],
>    Flatten[ReplaceList[#,{x___,y_,z___}->{x,Flatten[{y,n}],z}]&,
> 	HorseRaces[n-1]],1]
> 	]
> Unfortunately, Mathematica seems to ignore the Flatten[{y,n}] command,
> returning 
> {y,n} unflattened.  However, this only gives some unambiguous extra
> nesting in the solutions.

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