 The Gemara asked whether the proposition that a firstborn son takes a double portion only in the estate of his father might apply only in the case where a bachelor married a widow (who had children from her first marriage, and thus the father's firstborn son was not that of the mother).And thus where a bachelor married a virgin (so that the firstborn son of the father would also be the firstborn son of the mother) might the firstborn son also take a double portion in his mother's estate?Rav Nahman bar Isaac replied that says, "for he [the firstborn son] is the first-fruits of his [the father’s] strength," from which we can infer that the law applies to the first fruits of the father's strength and not the first-fruits of the mother's strength.