1. There is exactly one point in the intersection l f ? l e . Call this point z. Then, applying ADC to e and 1;P O By;there are exactly two possible cases: Case 1 : ? < 0 and ? > 0 (see Figure 4)
2. There is exactly one point in the intersection l f ? l d . Call this point z. Then, applying ADC to d and 1, we conclude that �(S, z) = 1. On the other hand, applying ADC to f and (1 + ?, 1 + ?);Case 2 : ? > 0 and ? < 0