... terminal and terminal symbols of Gw. This trans- forms the question of determining whether a symbol is useful into a reachibility question on the graph of Ma In particular, for any string of ... corresponding nodes in/ 3. The remaining nodes in 7 ~ have the constraints of the corresponding nodes in 7. Given p E dom(7), by Ibl(7,p) we refer to the label of the node addressed # in 7. Similarly, ... Weir, in pressa]. Definition 3.1 A LIG, G, is denoted G = ( Vjv , VT , VI , S, P ) where Vlv is a finite set of nonterminals, VT is a finite set of terminals, VI is a finite set of indices...