Published online by Cambridge University Press: 13 December 2021
We use an extension of Gordon–Litherland pairing to thickened surfaces to give a topological characterization of alternating links in thickened surfaces. If $\Sigma$ is a closed oriented surface and $F$
is a compact unoriented surface in $\Sigma \times I$
, then the Gordon–Litherland pairing defines a symmetric bilinear pairing on the first homology of $F$
. A compact surface in $\Sigma \times I$
is called definite if its Gordon–Litherland pairing is a definite form. We prove that a link $L$
in a thickened surface is non-split, alternating, and of minimal genus if and only if it bounds two definite surfaces of opposite sign.
Please note a has been issued for this article.