Searching for a Greek grammar PDF for the "Liceo Classico" for free leads to several digital libraries, school repositories, and open educational projects. While full copyright-protected modern textbooks are rarely available for free legal download, there are numerous high-quality alternatives for study and review. Comprehensive Manuals and Textbooks (PDF)
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While it's difficult to pinpoint a single, definitive resource, here are some potential sources that may satisfy the search query:
(V. Inama): Un testo storico in due volumi (Etimologia e Sintassi) disponibile su Archive.org. Esercizi di stile e di sintassi greca
Ideali per il ripasso veloce o il recupero, queste risorse sono create da docenti e licei: Schede grammaticali della Prof.ssa Orrù