(geometry) A statement in Euclidean geometry that deals with the construction of a particular parallelogram (the Varignon parallelogram) from an arbitrary quadrilateral.

(mathematics) Any of a collection of theorems of finite group theory that give detailed information about the number of subgroups of fixed order that a given finite group contains.

(mathematics) A statement in algebraic geometry concerning the number of common zeros of n polynomials in n indeterminates. In its original form, the theorem states that in general the number of common zeros equals the product of the degrees of the polynomials.

(mathematics) In additive combinatorics, a central result that indicates the approximate structure of sets whose sumset is small. It roughly states that if |A+A|/|A| is small, then A can be contained in a small generalized arithmetic progression.

(physics) A theorem that relates the time derivative of the expectation values of the position and momentum operators x and p to the expectation value of the force F=-V'(x) on a massive particle moving in a scalar potential V(x).

(mathematics) The two-dimensional counterpart of the ham sandwich theorem.

(logic, mathematics) One of two theorems in mathematical logic that demonstrates the inherent limitations of every formal axiomatic system containing basic arithmetic.

(mathematics) the theorem that there is at least one prime number between n and 2n for every n>1, i.e.:

(mathematics) A theorem stating that there is no nonvanishing continuous tangent vector field on the sphere; colloquially, that "you can't comb a hairy ball flat without creating a cowlick".

(statistics and mathematics, singular only) The theorem that states that if the sum of independent identically distributed random variables has a finite variance, then it will be approximately normally distributed.