Mathematics/Combinatorics

The Plünnecke-Ruzsa Inequality
by Angeliki Koutsoukou-Argyraki and Lawrence C. Paulson

Clique is not solvable by monotone circuits of polynomial size
by René Thiemann

Fisher's Inequality: Linear Algebraic Proof Techniques for Combinatorics
by Chelsea Edmonds and Lawrence C. Paulson

Enumeration of Equivalence Relations
by Emin Karayel

Roth's Theorem on Arithmetic Progressions
by Chelsea Edmonds, Angeliki Koutsoukou-Argyraki and Lawrence C. Paulson

Szemerédi's Regularity Lemma
by Chelsea Edmonds, Angeliki Koutsoukou-Argyraki and Lawrence C. Paulson

Combinatorial Design Theory
by Chelsea Edmonds and Lawrence C. Paulson

Van der Waerden's Theorem
by Katharina Kreuzer and Manuel Eberl

The Sunflower Lemma of Erdős and Rado
by René Thiemann

Cofinality and the Delta System Lemma
by Pedro Sánchez Terraf

Ordinal Partitions
by Lawrence C. Paulson

The Nash-Williams Partition Theorem
by Lawrence C. Paulson

Matroids
by Jonas Keinholz

The Falling Factorial of a Sum
by Lukas Bulwahn

The Twelvefold Way
by Lukas Bulwahn

Cardinality of Multisets
by Lukas Bulwahn

Catalan Numbers
by Manuel Eberl

Cardinality of Equivalence Relations
by Lukas Bulwahn

Spivey's Generalized Recurrence for Bell Numbers
by Lukas Bulwahn

Cardinality of Number Partitions
by Lukas Bulwahn

Cardinality of Set Partitions
by Lukas Bulwahn

Latin Square
by Alexander Bentkamp

Euler's Partition Theorem
by Lukas Bulwahn

Derangements Formula
by Lukas Bulwahn

Discrete Summation
by Florian Haftmann

Open Induction
by Mizuhito Ogawa and Christian Sternagel

Bondy's Theorem
by Jeremy Avigad and Stefan Hetzl

Well-Quasi-Orders
by Christian Sternagel

Hall's Marriage Theorem
by Dongchen Jiang and Tobias Nipkow

Ramsey's theorem, infinitary version
by Tom Ridge