  The left-corner transform removes left-recursion from (probabilistic)
context-free grammars and unification grammars, permitting simple top-down
parsing techniques to be used. Unfortunately the grammars produced by the
standard left-corner transform are usually much larger than the original. The
selective left-corner transform described in this paper produces a transformed
grammar which simulates left-corner recognition of a user-specified set of the
original productions, and top-down recognition of the others. Combined with two
factorizations, it produces non-left-recursive grammars that are not much
larger than the original.
