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You owe it to yourself to see The Odyssey on the biggest screen possible. I thought was a masterpiece after seeing it projected in a typical theater on 70mm film. But that was nothing compared to IMAX. An opening shot of the Trojan Horse buried on a beach towered above the audience. An aerial view of Odysseus's cliffside home in Ithaca took my breath away.

The belief revision field is opulent in new proposals and indigent in analyses of existing approaches. Much work hinge on postulates, employed as syntactic characterizations: some revision mechanism is equivalent to some properties. Postulates constraint specific revision instances: certain revisions update certain beliefs in a certain way. As an example, if the revision is consistent with the current beliefs, it is incorporated with no other change. A postulate like this tells what revisions must do and neglect what they can do. Can they reach a certain state of beliefs? Can they reach all possible states of beliefs? Can they reach all possible states of beliefs from no previous belief? Can they reach a dogmatic state of beliefs, where everything not believed is impossible? Can they make two conditions equally believed? An application where every possible state of beliefs is sensible requires each state of beliefs to be reachable. An application where conditions may be equally believed requires such a belief state to be reachable. An application where beliefs may become dogmatic requires a way to make them dogmatic. Such doxastic states need to be reached in a way or another. Not in specific way, as dictated by a typical belief revision postulate. This is an ability, not a constraint: the ability of being plastic, equating, dogmatic. Amnesic, correcting, believer, damascan, learnable are other abilities. Each revision mechanism owns some of these abilities and lacks the others: lexicographic, natural, restrained, very radical, full meet, radical, severe, moderate severe, deep severe, plain severe and deep severe revisions, each of these revisions is proved to possess certain abilities.

Forgetting a specific belief revision episode may not erase information because the other revisions may provide or entail the same information. Whether it does was proved coNP-hard for sequences of two arbitrary lexicographic revisions or arbitrarily long lexicographic Horn revisions. A polynomial algorithm is presented for the case of two lexicographic Horn revision. Heterogeneous sequences, including revisions other than lexicographic, were proved to belong in Delta2. Their previously proved coNP-hardness is enhanced to Dp-hardness.

The first of many planned IMAX theaters dedicated to virtual reality has opened in Los Angeles. Trading large, wraparound screens for small, immersive headsets, the facility allows anyone to experience VR without buying a high-end gaming PC or video game console. As UploadVR reports, the LA center has a mixture of HTC Vive and Starbreeze StarVR headsets. They're stored in 14 isolated "pods" which also contain a Dbox cinema chair, a vibration-emitting Subpac vest and a variety of physical controllers. You can buy experiences individually, such as John Wick Chronicles, or grab a "sampler" if you want a broader taste of VR.