3. The method of claim 2 wherein the steps of pruning the directed edge and deriving the pruned grammar are repeated iteratively until a stopping condition is met.
3. The method of claim 2 wherein the steps of pruning the directed edge and deriving the pruned grammar are repeated iteratively until a stopping condition is met. 4. The method of claim 3 wherein the stopping condition is the length of the expanded starting variable (s 0,i ) of the pruned grammar (G i ) being less than or equal to a predetermined length.