DJVU PDF Fallahi, M.M. 1992, "Present perfect simple and progressive tenses in English and Persian: a contrastive analysis of linguistic systems", in The Third International Symposium on Language and Linguistics, Bangkok, Thailand, pp. 747-755. Chulalongkorn University. cite.

DJVU PDF Jahangiri, N. 1992, "Some sociolinguistic aspects of Persian language", in The Third International Symposium on Language and Linguistics, Bangkok, Thailand, pp. 1393-1407. Chulalongkorn University. cite.

DJVU PDF Jahangiri, N. 1996, "Language change in time and space", in The Fourth International Symposium on Language and Linguistics, Thailand, pp. 1906-1914. Institute of Language and Culture for Rural Development, Mahidol University. cite.