in his initial days he studied VD Mahajan's book, as you mentioned in your reply, later on he consulted internet for preparation of notes, here the most important point which is to be noted that he did not studied Mahajan book completely rather he relied upon important events, topics and mostly the repeated questions of past papers.

make a list of topic, scrutinize whole syllabi of the subject then make an outline of every question that may seem important to you. rest assured if you had have time then describe the answer of each question with short notes.

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----''Alexander''----