  A simple linear-time algorithm for constructing a linear context-free tree
grammar of size O(rg + r g log (n/r g))for a given input tree T of size n is
presented, where g is the size of a minimal linear context-free tree grammar
for T, and r is the maximal rank of symbols in T (which is a constant in many
applications). This is the first example of a grammar-based tree compression
algorithm with a good, i.e. logarithmic in terms of the size of the input tree,
approximation ratio. The analysis of the algorithm uses an extension of the
recompression technique from strings to trees.
