Using \textstyle as default with amsmath environments?

Question

I want to use \textstyle as the default in my amsmath equations, while retaining \displaystyle as unchanged command for compatibility across documents.

Apparently, amsmath hardcodes the use of \displaystyle and thus in [ \textstyle as default method of displaying mathematics ] it was recommended to use \let\displaystyle\textstyle to achieve this.

Is there any possibility to make \textstyle the default, without redefining \displaystyle?

Answer 1

Since amsmath hardcodes some environments to explicitly use \displaystyle, you must redefine \displaystyle to be \textstyle as @DavidCarlisle said in your linked post.

But, just in case you need to re-use \displaystyle, then issue \let\olddisplaystyle\displaystyle before \let\displaystyle\textstyle to reserve the original \displaystyle in \olddisplaystyle.