# compactness

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**List of philosophy topics (A-C)**— 110th century philosophy 11th century philosophy 12th century philosophy 13th century philosophy 14th century philosophy 15th century philosophy 16th century philosophy 17th century philosophy 18th century philosophy 19th century philosophy220th… …82

**Glossary of topology**— This is a glossary of some terms used in the branch of mathematics known as topology. Although there is no absolute distinction between different areas of topology, the focus here is on general topology. The following definitions are also… …83

**Locally compact space**— In topology and related branches of mathematics, a topological space is called locally compact if, roughly speaking, each small portion of the space looks like a small portion of a compact space.Formal definitionLet X be a topological space. The… …84

**Orthogonality**— The line segments AB and CD are orthogonal to each other. Orthogonality occurs when two things can vary independently, they are uncorrelated, or they are perpendicular. Contents 1 Mathematics …85

**König's lemma**— or König s infinity lemma is a theorem in graph theory due to Dénes Kőnig (1936). It gives a sufficient condition for an infinite graph to have an infinitely long path. The computability aspects of this theorem have been thoroughly investigated… …86

**Logical implication**— In logic and mathematics, logical implication is a logical relation that holds between a set T of formulae and a formula B when every model (or interpretation or valuation) of T is also a model of B . In symbols,# T models B, # T Rightarrow B # T …87

**Zariski topology**— In algebraic geometry, the Zariski topology is a particular topology chosen for algebraic varieties that reflects the algebraic nature of their definition. It is due to Oscar Zariski and took a place of particular importance in the field around… …88

**Second-order logic**— In logic and mathematics second order logic is an extension of first order logic, which itself is an extension of propositional logic.[1] Second order logic is in turn extended by higher order logic and type theory. First order logic uses only… …89

**List of mathematical logic topics**— Clicking on related changes shows a list of most recent edits of articles to which this page links. This page links to itself in order that recent changes to this page will also be included in related changes. This is a list of mathematical logic …90

**Σ-compact space**— In mathematics, a topological space is said to be sigma; compact if it is the union of countably many compact subspaces. A space is said to be sigma; locally compact if it is both sigma; compact and locally compact.Properties and Examples* Every… …