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Rational[a,b] vs Rational[1,2]

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  • Subject: [mg116618] Rational[a,b] vs Rational[1,2]
  • From: Richard Fateman <fateman at>
  • Date: Mon, 21 Feb 2011 19:30:54 -0500 (EST)

I find it potentially hazardous that Head[]
does not distinguish the cases of Head[1/2]

and Head[Rational[a,b]]

Thus these both get transformed...

1/2  /. Rational[r_,s_]-> foo[r,s]

Rational[a,b] /. Rational[r_,s_] -> foo[r,s]

but compare ...

1/2  /. 2->4

Rational[a,2] /. 2->4

I'm not saying I'm surprised by this, of course.

Perhaps Rational[a,b] should be converted to a/b unless both
a and b are numbers.

Oh, for some fun, try Rational[1/2,4].


PS, I used version 7.

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