Let $\mathcal{C}$ be a complexity class and $A$ be a language. The statement ``$A \not\in \mathcal{C}$'' is a separation of $A$ from $\mathcal{C}$. A separation is constructive if there is an efficient algorithm called a refuter that prints counterexamples to the statement ``$M$ decides $A$'' for every $\mathcal{C}$-algorithm $M$. Concretely, ... more >>>

The complexity class PPP contains all total search problems many-one reducible to the PIGEON problem, where we are given a succinct encoding of a function mapping n+1 pigeons to n holes, and must output two pigeons that collide in a hole. PPP is one of the “original five” syntactically-defined subclasses ... more >>>

We give a new characterization of the Sherali-Adams proof system, showing that there is a degree-$d$ Sherali-Adams refutation of an unsatisfiable CNF formula $C$ if and only if there is an $\varepsilon > 0$ and a degree-$d$ conical junta $J$ such that $viol_C(x) - \varepsilon = J$, where $viol_C(x)$ counts ... more >>>