I’ve found that indenting is best achieved either by using an indent environment (
\indent, then hit enter), or by using spaces. To get a tab-length-ish space in a mathematical formula, press space, then hit tab several times until the space gets as long as you’d like it to be! You can also edit the value of the space to whatever you like.
You can also create a custom “tab length” space shortcut: type
\assign, hit enter, then call it whatever you like in the first argument (e.g. we’ll call it simply
tab), then in the second argument type
\space, hit enter, then type
1tab, then hit enter twice. After that point in the document (and not before), typing
\tab and hitting enter should give you a tab-length space. I’m not sure if there are better shortcuts…