mjhjmtu

I have trouble getting a nice symbol for the set of non-squares. I would like to have a crossed out square, but the

$notsquare$

command does not place the line at the right place.

Using the package centernot it gets a little better

usepackagecenternot
$centernotsquare$

Now the line is at the right place but it is not as symmetric as it should be: the line comes only just up to the top side of the square. Any ideas?

You can define your own symbol as an overlay of square with / using ooalign:

documentclassarticle

usepackageamssymb

newcommandnotsquare
 mathrel
 ooalign
 $square$cr
 hidewidthraise.225exhbox$/$hidewidth
 
 


begindocument

[
 f mathrelsquare g notsquare h
]

enddocument

Here is a short course on ooalign: subseteq + circ as a single symbol ("open subset")

Since not is made to apply to math relations, a better syntax would be mathordnotmathrelsquare. However, while that fixes the horizontal placement, vertical is still not ideal.

So I propose a "BEST" stackengine approach.

However, the OP notes the desire to avoid extra packages so I edited to also provide a native Alternative.

documentclassarticle
usepackageamssymb,stackengine
begindocument
[
textrmBetter: quadmathordnotmathrelsquare
]
[
textrmBest: quadensurestackMathstackinsetcc/square
]
[
textrmAlternative: quadraisebox1pt$notmathrelraisebox-1pt$square$$
]
enddocument