We present an algorithm for computing a maximum agreement subtree of two
unrooted evolutionary trees. It takes O(n^{1.5} log n) time for trees with
unbounded degrees, matching the best known time complexity for the rooted case.
Our algorithm allows the input trees to be mixed trees, i.e., trees that may
contain directed and undirected edges at the same time. Our algorithm adopts a
recursive strategy exploiting a technique called label compression. The
backbone of this technique is an algorithm that computes the maximum weight
matchings over many subgraphs of a bipartite graph as fast as it takes to
compute a single matching
