A differential ideal is a concept from the field of differential algebra, which studies algebraic structures that are equipped with a derivation (a generalization of the idea of differentiation). In this context, a derivation is a unary operation that satisfies the properties of linearity and the Leibniz rule (product rule). ### Definition: A differential ideal is a special type of ideal in a differential ring (a ring equipped with a derivation) that is closed under the action of the derivation.
Martin measure is a concept from the field of probability theory and stochastic processes, particularly in relation to potential theory and the study of Markov processes. It is named after the mathematician David Martin, who made significant contributions to these areas. In the context of Markov processes, the Martin measure is often associated with edge-reinforced random walks and other stochastic models where one is interested in understanding the long-term behavior of the process.