Figure 9

Fragment of a binary choice tree (ovals) superimposed on grammar (identical to Figure 4). Unfilled ovals mean left hand production "0" is to be taken. Shaded ovals indicate right hand production "1" is expanded. Using the BNF grammar shown in Figure 8, the first choice rule following <start> (top) is <RE>. <RE> has two options: <union> and <simple-RE>. This evolved grammar (Figure 4) uses first option (<union>). Hence the first <RE> oval is not filled and the first bit of the equivalent bit string is "0". Thus this tree fragment represents the binary choices: 00 ... 0111111110000111111111111111011101100111010101.