Named for this person are a theorem stating that every positive integer is 
Named for this person are a theorem stating that every positive integer is the sum of four squares; a theorem that states that, given a finite group G with a subgroup H, the cardinality of H divides the cardinality of G; and the stationary solutions of the circle-restricted three body problem. In his namesake formulation of mechanics, one calculates trajectories by minimizing the action, and the energy function central to that formulation is also named for him and is symbolized L. For ten points, all of these nifty things are named after what mathematician who also demonstrated the mean value theorem.
Named for this person are a theorem stating that every positive integer is the sum of four squares; a theorem that states that, given a finite group G with a subgroup H, the cardinality of H divides the cardinality of G; and the stationary solutions of the circle-restricted three body problem.
Joseph Louis {Lagrange} (or Giuseppe Luigi {Lagrangia})