Let C be a nonfaulty bivalent configuration, let  = (x,m) be a noncrash event that is applicable to C; let A be the set of nonfaulty configurations reachable from C without applying , and let B{(A) | A ∈ A}. Prove that if B does not contain any bivalent configuration, then it contains both 0-valent and 1-valent configurations.