       Re: Hold and Equal

• To: mathgroup at smc.vnet.net
• Subject: [mg73734] Re: Hold and Equal
• From: dh <dh at metrohm.ch>
• Date: Tue, 27 Feb 2007 05:41:50 -0500 (EST)
• References: <erufqm\$s7j\$1@smc.vnet.net>

```
Hi Murray,

a quick and dirty solution that does not create evaluation problems is

to convert your expression into a string and make the replacement there:

fun[x_]:= StringReplace[ToString[x], "==" -> "="]

if you now say: fun[(a + b)^2 == Expand[(a + b)^2]] you get:

2     2            2

(a + b)  = a  + 2 a b + b

Daniel

Murray Eisenberg wrote:

> How can I produce in an Output cell (under program control) an

> expression like the following,

>

>    (a+b)^2 = a^2+ 2 a b + b^2

>

> where instead of the usual Equal (==) I get a Set (=), as in traditional

> math notation?  I want to input the unexpanded (a+b)^2 and have the

> expansion done automatically.

>

> Of course, I can try something like the following:

>

>    (a+b)^2 == Expand[(a+b)^2])

>

> So how do I convert the == to =?  Of course

>

>    ((a + b)^2 == Expand[(a + b)^2]) /. Equal -> Set

>

> gives a Set::write error.  And

>

>    (Hold[(a + b)^2 == Expand[(a + b)^2]]) /. Equal -> Set

>

> doesn't actually evaluate the Expand part and leaves the "Hold" wrapper.

>

>

>

>

```

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