I have come across this Engineering Mathematics book Higher Engineering Mathematics by B. S. Grewal and wanted to go into details of a sub-topic not keenly mentioned in any other related books. However, I realized that this book, which is extensively used as Mathematics textbook for about the 200 engineering colleges I know in Delhi NCR (India) since 1990s, does not have any References section.

Am I uninformed here? Is there supposed to be a separate URL providing references?

Is it a convention to not include this section in Textbooks?

What should I do in such cases?