Reference for Keritot 28:4

נשאת לאחיו מיגו דאיתוסף איסור לגבי אחין איתוסף איסורא לגבי דידיה

When she marries his brother, since she becomes prohibited also to his other brothers,<span class="x" onmousemove="('comment',' Viz., his half-brothers of a common father. Before her marriage to one of them she was permitted to all of them, except her own father.');">³</span>

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