Reference for Sanhedrin 150:4

אלא אם חמיו ואם חמותו כחמותו האי למטה כלמעלה למעלה כלמטה הואי תני למעלה כלמטה

The Master said: 'Whence do we know that the lower is as the upper?' What is meant by 'lower' and 'upper'? Shall we say that her son's daughter and her daughter's daughter ['lower'] are as her own daughter ['upper']?<span class="x" onmousemove="('comment',' So that 'lower' and 'upper' refer to the order of generations: 'lower', the third generation in the downward direction, viz. her son's daughter and her daughter's daughter; 'upper', one generation above them, viz., her daughter. ');">⁴</span>

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