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Re: Pattern matching


On 2/6/2011 2:35 AM, StatsMath wrote:
> Have a question regarding the applicaiton of pattern rules:
>
> fact[4] //. {fact[n_] :>  n fact[n-1], fact[0] ->  1}
>
> This is a bug since fact[0] needs to be defined 1st, but I expected
> the above to grind away idefnitely but it returned a a value 0,
> instead of an infininte computation.
>
> Can you help me understand why the above returns 0?
>
> Thanks!
>
it looks to me like
fact[0] is replaced by  0*fact[-1] which is simplified to 0.  the other 
rule isn't seen.



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