Can I define $⊂=$ to show as $subset.eq$?

[quachpas]

Hello!
To define a shortcut for ⊆, you can simply define a variable

#let sse = math.subset.eq
$
  sse
  subset.eq
$

As you said, writing a variable can only be defined within specific naming constraints. See

• What characters may the names of variables and functions consist of?.
• What are the rules for identifiers in Typst? - #2 by xkevio