Alexander module of a connected sum
= Alexander module of a connected sum
{c}
{title2=$\mathcal A_{K\#J}\cong\mathcal A_K\oplus\mathcal A_J$}
Boundary-connected-summing <Seifert surfaces> gives a block-diagonal <Seifert matrix>, because basis curves in the separated summands have zero linking. The <Seifert-matrix presentation of the Alexander module> is block diagonal too. Thus the Alexander <modules> form a direct sum and their <Alexander polynomials of a knot> multiply up to a unit.