Tarski's undefinability theorem is a result in mathematical logic that deals with the concept of truth within formal languages. Named after the logician Alfred Tarski, the theorem asserts that the notion of truth cannot be defined within a sufficiently expressive formal language that can express arithmetic truths about itself.

The Szpilrajn extension theorem, also known as the Szpilrajn-Sierpiński extension theorem, is a result in order theory, specifically within the area concerning partially ordered sets (posets). The theorem provides a method for extending a given partial order to a total order.

The Schröder–Bernstein theorem is a fundamental result in set theory that provides a criterion for the existence of a bijection (one-to-one and onto correspondence) between two sets, given certain conditions about the existence of injections (one-to-one functions) between those sets. In the context of measurable spaces, the theorem can be reformulated to pertain to the measurability of the functions involved.

Robinson's joint consistency theorem is a result in the field of decision theory and economics related to the consistency of preferences and the representation of preferences by a utility function. The theorem addresses the question of how to represent preferences over a set of choices that may vary according to certain parameters. Specifically, it deals with the conditions under which a joint distribution of choices can be consistent with the preferences of agents when making those choices.

Richardson's theorem is a result in the field of mathematical logic, specifically in the area of computability theory. The theorem states that if \( A \) is a recursively enumerable (r.e.) set, then the set of its recursive subsets is r.e. This theorem has significant implications for understanding the structure of recursively enumerable sets and their relationships to recursive sets. In more technical terms, the theorem provides a comprehensive characterization of the recursive subsets of a recursively enumerable set in terms of effective enumerability.

The Rice–Shapiro theorem, often referred to as Rice's theorem in the context of computability theory, is a fundamental result concerning the properties of recursively enumerable (r.e.) sets and the functions computable by Turing machines. In its standard form, Rice's theorem states that any non-trivial property of the languages recognized by Turing machines is undecidable.

Rice's theorem is a fundamental result in computability theory that addresses the limits of what can be determined about the behavior of Turing machines and languages recognized by them. Specifically, the theorem states that any non-trivial property of the languages recognized by Turing machines is undecidable.

Post's theorem, named after Emil Post, is a result in the field of mathematical logic and computability theory. It specifically deals with the properties of recursively enumerable sets, particularly in the context of formal languages and decision problems. The theorem states that: **"For any countable set of recursive (or computable) functions, there exists a recursively enumerable set that captures all the functions from the set.

The Paris–Harrington theorem is a result in the field of mathematical logic and combinatorics, specifically in the area of set theory and the study of large cardinals. It is a form of combinatorial principle that exemplifies the limits of certain deductive systems, particularly in relation to the axioms of Peano arithmetic and other standard set theories.

Löb's theorem is a result in mathematical logic, particularly in the area concerning formal systems and provability. It deals with self-referential statements in formal systems and is often discussed in the context of Gödel's incompleteness theorems.

Lusin's separation theorem is an important result in the field of measure theory and topology, particularly in the context of Borel sets and measurable functions. The theorem deals with the separation of measurable sets by continuous functions.

Lindström's theorem is a significant result in model theory, a branch of mathematical logic that deals with the relationships between formal languages and their interpretations, or models. Formulated by Per Lindström in the 1960s, the theorem characterizes the logical systems that enjoy certain completeness and categoricity properties, specifically those known as the "Lindström properties.

The Knaster-Tarski theorem is a fundamental result in the field of fixed-point theory, particularly in the context of partially ordered sets (posets).

Kleene's recursion theorem, named after mathematician Stephen Cole Kleene, is a fundamental result in the field of computability theory. It addresses the existence of computable functions that can be defined recursively. The theorem states that for any total computable function \( f \), there exists a program (or particular index in the sense of the arithmetical hierarchy) that produces itself as an output when given its own index (or code) as input.

The Kanamori–McAloon theorem is a result in the field of combinatorial optimization and discrete mathematics, particularly related to the study of perfect matchings in bipartite graphs. It is named after researchers Yoshihiro Kanamori and Jim McAloon. While the specific theorem may not be universally recognized or widely published under that name, it typically pertains to conditions under which certain structured forms of bipartite graphs possess perfect matchings.

Herbrand's theorem is an important result in mathematical logic, particularly in the field of model theory and proof theory. It connects syntactic properties of first-order logic formulas to semantic properties of their models. There are several formulations of Herbrand's theorem, but one of the most common versions concerns the existence of models for a set of first-order logic sentences. ### Herbrand's Theorem (Informal Statement) 1.

Gödel's speed-up theorem is a result in the field of mathematical logic, particularly in the study of formal systems and computability. It essentially states that for certain mathematical statements that can be proven in a relatively weak formal system, there exist stronger systems in which those statements can be proven more efficiently—specifically, in what is known as "faster" or more succinct proofs.

Frege's theorem is a significant result in the foundations of mathematics and logic, attributed to the German mathematician and philosopher Gottlob Frege. It establishes the connection between logic and mathematics, specifically concerning the foundations of arithmetic. At its core, Frege's theorem asserts that the basic propositions of arithmetic can be derived from purely logical axioms and definitions. More specifically, it shows that the arithmetic of natural numbers can be defined in terms of logic through the formalization of the concept of number.

"Extension by new constant and function names" usually refers to a concept in formal logic and model theory, particularly in the context of extending a theory by adding new symbols for constants and functions. In formal logic, a theory can be thought of as a set of sentences in a formal language. Sometimes, one needs to expand or extend the language of the theory to include additional elements. Here's how this works in practice: 1. **New Constants**: You can introduce new constant symbols into the language.