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This is a part of a series. The main series, written by Zbigniew Nienacki himself, consists of 15 books. After his death in 1994 it has been continued by various authors, and it consists now some 160+ books, with the main protagonist, Mr. Automobile has been not used after book 106, with his disciple taking the main role completely.

Thank you so much for the explanation.

Makes sense now