identity+in+quantity
131Price discrimination — or price differentiation[1] exists when sales of identical goods or services are transacted at different prices from the same provider.[2] In a theoretical market with perfect information, perfect substitutes, and no transaction costs or… …
132Perturbation theory (quantum mechanics) — In quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one. The idea is to start with a simple system for which a …
