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Published online by Cambridge University Press: 15 December 2025
We show that any two same-genus, oriented, boundary parallel surfaces bounded by a non-split, alternating link into the 4-ball are smoothly isotopic relative to the boundary. In other words, any same-genus Seifert surfaces for a non-split, alternating link become smoothly isotopic relative to the boundary once their interiors are pushed into the 4-ball. We conclude that a smooth surface in
$S^4$ obtained by gluing two Seifert surfaces for a non-split alternating link is always smoothly unknotted.