       Re: Q: How to force an Equal[]

• To: mathgroup at smc.vnet.net
• Subject: [mg3363] Re: [mg3332] Q: How to force an Equal[]
• From: Richard Mercer <richard at seuss.math.wright.edu>
• Date: Sat, 2 Mar 1996 04:12:34 -0500
• Sender: owner-wri-mathgroup at wolfram.com

```>  Hi there,
>

>  this should be a nice relaxing one. How can I force Mma
>  to evaluate the equal expression, regardless of what
>  values Word or Number stand for. I just want a false in
>  the second case (y1==y2).
>  ......

I learned a long time ago to use == ONLY for numerical equalities and
use === for other things. The truth is not quite that simple, but this
simple rule will generally keep you out of trouble. Also avoid using ==
with exact numerical expressions, e.g. with
a = 2 + Sqrt; b = 2/(2 - Sqrt);
a == b   does not evaluate.
a === b  gives False
N[a] == N[b] gives True

So y1 === y2 ought to do the trick here. (Haven't tried it.)
You can also use TrueQ[y1==y2] to force a decision. This always yields
True or False, defaulting to False.

Richard Mercer

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