       Re: Hold and Equal

• To: mathgroup at smc.vnet.net
• Subject: [mg73745] Re: Hold and Equal
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Tue, 27 Feb 2007 05:47:49 -0500 (EST)
• References: <erufqm\$s7j\$1@smc.vnet.net>

```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.
>
>
>
>
Murray,

Here is one way - creating the expression at the box level:

x=(a+b)^2

RowBox[{ToBoxes[x],"=",ToBoxes[Expand[x]]}]//DisplayForm

David Bailey
http://www.dbaileyconsultancy.co.uk

```

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