A criterion

for judging of writing in a math textbook. Assume all of the arguments in the textbook are correctly stated.

If, reading only the definitions and statements of theorems, lemmas, etc., (stuff typeset in a theorem environment) along with the material that is not any of those or contained in a proof, one is then able to accurately characterize the goals and meta-arguments of the text, then the textbook is well written.

Carry on.