(Devarim 13:13) " If you hear": There is no need to press an inquiry. I might think, then, that one need not pursue it, (even if he did hear); it is, therefore, written (15) "And you shall inquire, and you shall search out, and you shall ask well." "in one of your cities": one city is made "a condemned city," and not three. I might think, not even two; it is, therefore, written "your cities." "which the L-rd your G-d gives to you": to exclude (cities) outside of Eretz Yisrael. "to dwell there": to exclude Jerusalem, which was not apportioned (among the tribes) for dwelling.
Sifrei Devarim 92
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