   These first two ways of amending the RTT both, in effect, restrict the notion of a revision sequence, by putting constraints on which of our revision sequences really count as acceptable revision sequences. The constraints are, in some sense local: the first constraint is achieved by putting restrictions on which hypotheses can be used, and the second constraint is achieved by putting restrictions on what happens at limit ordinals. A third option would be to put more global constraints on which putative revision sequences count as acceptable. Yaqūb 1993 suggests, in effect, a limit rule whereby acceptable verdicts on unstable sentences at some limit stage η depend on verdicts rendered at other limit stages. Yaqūb argues that these constraints allow us to avoid certain “artifacts”. For example, suppose that a ground model M = &lt;D, I &gt; has two independent liars, by having two names α and β, where I(α) = ¬Tα and I(β) = ¬Tβ. Yaqūb argues that it is a mere “artifact” of the revision semantics, naively presented, that there are revision sequences in which the sentence ¬Tα ≡ ¬Tβ is stably true, since the two liars are independent. His global constraints are developed to rule out such sequences. (See Chapuis 1996 for further discussion.) 