  Given a string $T$ with length $n$ whose characters are drawn from an ordered
alphabet of size $\sigma$, its longest Lyndon subsequence is a longest
subsequence of $T$ that is a Lyndon word. We propose algorithms for finding
such a subsequence in $O(n^3)$ time with $O(n)$ space, or online in $O(n^3
\sigma)$ space and time. Our first result can be extended to find the longest
common Lyndon subsequence of two strings of length $n$ in $O(n^4 \sigma)$ time
using $O(n^3)$ space.
