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Re: Head logic

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97056] Re: [mg97033] Head logic
  • From: "David Park" <djmpark at comcast.net>
  • Date: Wed, 4 Mar 2009 07:11:37 -0500 (EST)
  • References: <26933028.1236078461072.JavaMail.root@m02>

In situations like this one ought really use SameQ and UnsameQ. True, in
this case one can't assign values to Symbol or Integer, but Mathematica is
clearly not using that fact and therefore does not know whether they are
Equal or not.


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  



From: carlos at colorado.edu [mailto:carlos at colorado.edu] 

Entering

   ClearAll[r];
   Head[r]
   Head[r]!=Symbol
   Head[r]==Symbol

give Symbol, False and True as expected. But

   Head[r]==Integer

evaluates to Symbol==Integer. Why not False?
Head[r] is certainly not Integer. Likewise

  r=4;
  Head[r]==Integer
  Head[r]!=Symbol
  Head[r]==Symbol

give True (correct) but  Integer!=Symbol and Integer==Symbol.
Why not True and False?




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