同©大学 TONGJI UNIVERSITY o Because when a equal b,means a output equal b output.When b equal c,means b output equal c output.If output of b is indefinite,b output value can change if b equals a or equals c,so b can not equal a and c at the same time⚫Because when a equal b, means a output equal b output. When b equal c, means b output equal c output. If output of b is indefinite, b output value can change if b equals a or equals c, so b can not equal a and c at the same time