In model theory, a branch of mathematical logic, the Łoś–Vaught test is a criterion for a theory to be complete, unable to be augmented without becoming inconsistent. For theories in classical logic, this means that for every sentence, the theory contains either the sentence or its negation but not both.
A theory
T
\kappa
\kappa
T
\kappa.
The Łoś–Vaught test states that if a satisfiable theory is
\kappa
\kappa\geq|\sigma|
This theorem was proved independently by and, after whom it is named.