Compared to (Moschitti and Bejan, 2004) where tree fragments are heuristically extracted before applying tree kernels, the MOLT kernel is general and desirable since it does not require such fragment extraction.
3 We denote a marked ordered labeled tree where node n k of an ordered labeled tree U is marked by mark X, n l by Y , and so on, by U @{n k = X, n l = Y, .