The behavior of the Hasse–Schmidt algebra under étale extension is used to show that the Hasse–Schmidt algebra of a smooth algebra of finite type over a field equals the ring of differential operators. These techniques show that the formation of Hasse–Schmidt derivations does not commute with localization, providing a counterexample to a question of Brown and Kuan; their conjecture is reformula...

The last several months have raised public awareness of the extent of Internet monitoring by governments. The obvious defense is to use more cryptography, and in particular end-to-end encryption. This is done all too seldom, which in turn raises the question of why: why do so few sites, users, and protocols employ end-to-end encryption? Is there something that standards bodies such as the IETF ...

We study generalized amalgamation properties in simple theories. We state the definition of generalized amalgamation in such a way so that the properties are preserved under interpreted theories. To deal with the properties, new notions of generalized types and generalized Morley sequences are introduced. We consider several sub-hierarchies of simple theories that affect generalized amalgamatio...

Standard economic models of contract imply that contracts should be highly “complex,” by which we mean (1) rich in the expected number of payoff-relevant contingencies; (2) variable in the magnitude of payoffs contracted to flow between parties; and (3) severe in the cognitive load necessary to understand the contract. Yet most realworld contracts are simple along all three of these dimensions....

Both in learning and in natural science, one faces the problem of selecting among a range of theories, all of which are compatible with the available evidence. The traditional response to this problem has been to select the simplest such theory on the basis of “Ockham’s Razor”. But how can a fixed bias toward simplicity help us find possibly complex truths? I survey the current, textbook answer...