The claim that a firm's profit reaches its maximum value at the economic equilibrium point (where marginal revenue equals marginal cost in standard microeconomic theory) is a fundamental, textbook definition in economics, requiring no citation.
The retrieved papers cover macroeconomics, supply chains, microbial markets, AI chatbots, and mechanism design, none of which directly test or refute the standard microeconomic definition of profit maximization at equilibrium. Therefore, the claim is treated as a standard microeconomic definition (common knowledge), and no papers are placed in support or refutation.