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Topic: Truth in inequalities
Replies: 4   Last Post: Jun 16, 2001 3:02 AM

 Messages: [ Previous | Next ]
 Jack Goldberg Posts: 53 Registered: 12/7/04
Truth in inequalities
Posted: Jun 14, 2001 2:50 AM

Hi group,

Can someone explain the logic of the following:

x < Infinity returns x < Infinity
while
x - Infinity < 0 returns True

I should mention that I am aware of the fact that x - Infinity simplifies
automatically to -Infinity which is then compared to 0 and found wanting.
The issue I'm raising is why should a CAS that has x-Infinity < 0 return
True not also return True for the x < Infinity? One awkwardness of
having this difference of behavior can be seen in the example,

MyFunction[x_,y_]/;(x<y) := blah

and

MyFunction[x_,y_]/;(x-y<0) := blah

do not do the same thing when, say, y=Infinity.

Just curious :-)

Jack

Date Subject Author
6/14/01 Jack Goldberg
6/15/01 Erk Jensen
6/15/01 Andrzej Kozlowski
6/15/01 Orestis Vantzos
6/16/01 Mianlai Zhou