(quantum mechanics) A method of reducing high-order derivatives to a combinatorics problem, used extensively in quantum field theory to reduce arbitrary products of creation and annihilation operators to sums of products of pairs of these operators.

(group theory) The theorem stating that every group G is isomorphic to a subgroup of the symmetric group acting on G.

(mathematics) A basic result of algebraic topology, connecting homotopy theory with homology theory via a map known as the Hurewicz homomorphism.

(number theory) A theorem that gives a finite bound on the number of consecutive pairs of smooth numbers that exist, for a given degree of smoothness, and provides a method for finding all such pairs using Pell equations.

(number theory) A theorem stating that the sum of the reciprocals of the twin primes converges to a finite value (Brun's constant).

An important limitative theorem in quantum computing that establishes an upper bound (Holevo's bound) for the amount of information that can be known about a quantum state.

(mathematics) A result concerning certain infinite-dimensional vector spaces, stating that any orthomodular form that has an infinite orthonormal sequence is a Hilbert space over the real numbers, complex numbers or quaternions.

(politics) A theorem stating that no voting system can be perfectly fair in all circumstances

plural of spectral theorem

(mathematics) A theorem stating that any non-singular algebraic curve defined by algebraic number coefficients represents a compact Riemann surface which is a ramified covering of the Riemann sphere, ramified at three points only.