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The boundaries of Eastern Nahuatl are not clear. Southeastern Puebla (Tehuacan-Zongolica) is particularly ambiguous. Hasler (1996:164) summarizes the situation,
"Juan Hasler (1958:338) interprets the presence in the region of eastern dialect features and central dialect features as an indication of a substratum of eastern Nahuatl and a superstratum of central Nahuatl. Una Canger (1980:15–20) classifies the region as part of the eastern area, while Yolanda Lastra (1986:189–190) classifies it as part of the central area."