Figure 2

Homeomorphic Subtree Alignment. Thick lines represent tree edges, and dotted lines connect aligned node pairs. (a) An HSA A = {(a,a′),(b,b′),…,(f,f′)} between two trees T and S. The set of pruned subtrees (in green fillings) with respect to A is $\pi \left(A\right)=\left\{T_g^a,T_k^j,S_{h^{\prime }}^{b^{\prime }}\right\}$. The set of smoothed nodes (in lined red) with respect to A is δ(A) = {j,g′}. (b) The subtrees T′ and S′ of T and S, respectively, obtained after pruning the subtrees in π(A). (c) The smoothings T” and S” of T’ and S’, respectively, obtained after smoothing the nodes in δ(A). Mapping A is an isomorphic alignment between T” and S”.