BROWSE ALPHABETICALLY LEVEL:    Elementary    Advanced    Both INCLUDE TOPICS:    Basic Math    Algebra    Analysis    Biography    Calculus    Comp Sci    Discrete    Economics    Foundations    Geometry    Graph Thry    History    Number Thry    Phys Sci    Statistics    Topology    Trigonometry		generalized continuum hypothesis – Hempel’s Ravens Paradox generalized continuum hypothesis   The claim that there is no set of intermediate cardinality between any given set and its power set. The GCH is independent of (i.e., cannot be proved true or false by) the known axioms of set theory. Cf. continuum hypothesis. Related article: Gödel's Theorems Related MiniText: Infinity -- You Can't Get There From Here... genus   Topology: Given a topological surface S, the genus of S is the ordered pair (h, c) in which h is the number of handles on the surface and c is the number of cross-caps. Graph Theory: The genus of a graph is the minimum genus of the topological surface on which the graph can be drawn without crossovers. Intuitively, the minumum number of handles one must attach to a sphere to draw the graph on it. geodesic   A curve on a space is a geodesic if, given any two points on the curve, the segment of the curve joining the points is the shortest such curve. In Euclidean space, geodesics are straight lines. On a sphere, the geodesics are the great circles of the sphere. Graph Theory: A shortest path between two vertices is sometimes called a geodesic. Cf. distance. geometric series   An infinite series such that the ratio of consecutive terms is constant. Such a series may be denoted where r is the common ratio. A geometric series converges if and only if the common ratio is less than 1, in which case the sum of the series is given by Cf. arithmetic series, harmonic series. Related article: Series g.l.b.   Abbreviation for greatest lower bound. Kurt Gödel Gödel, Kurt   (1906 – 1978)   The foremost logician of the 20th century. He is famous for many deep results in the foundations of mathematics, including the Godel Completeness Theorem, the Godel Incompleteness Theorem, and that the generalized continuum hypothesis and the axiom of choice are consistent with the other axioms of set theory. He moved from Austria to the Institute for Advanced Study at Princeton, New Jersey, in 1940. He was a lifelong friend of Albert Einstein, and in the 1950’s formulated versions of Einstein’s relativity theories that permitted the logical possibility of time travel. Cf. logic Related article: Gödel's Theorems graph   General: A picture or diagram representing one or more relationships among certain objects or quantities. Functions: The collection of ordered tuples (x,y), consisting of domain elements x (possibly also tuples) and corresponding range elements y. Although informally we often mean the picture when we speak of the graph of a function, the graph should always be formally thought of as a set of tuples. Graph Theory: A collection of nodes (also called vertices), together with a set of edges joining the nodes. Formally, a graph G is a set of vertices V, a set of edges E, and a symmetric relation between them specifying incidence. Every edge must be incident on exactly two (not necessarily distinct) vertices, called its ends. Two vertices incident on the same edge are called adjacent. Graphs are often represented pictorially, with the vertices being points (or small circles or squares or some such), and the edges being curves (often line segments), with the endpoints of each such curve being the ends of that edge in the graph. Cf. Konigsberg Bridge Problem. great circle   On a sphere, a great circle is a circle containing the endpoints of a diameter of the sphere, that is, a circle of maximal size. A geodesic on a sphere always lies on a great circle. greatest common divisor   The greatest common divisor of two natural numbers a and b is the largest natural number c such that c divides a and c divides b. greatest lower bound   A lower bound which is greater than or equal to every other lower bound. Cf. Least upper bound. Greek    ARTICLE   Letters of the Greek alphabet are commonly used in mathematics. See the article for a full description. group   A set together with a binary operation defined on its elements, satisfying The group operation is associative, There is an identity element, i.e., an element e of the group so that for any other element a of the group we have ea = ae = a, and for every element a of the group there is an element a´, called the inverse of a, so that aa´ = a´a = e. If the group operation is commutative, the group is called Abelian. If the condition that every element have an inverse is dropped, the set is called a monoid. If in addition the requirement that an identity element exist is dropped, the set is called a semigroup. Finally, if the condition that the group operation be associative is dropped, the set is called a groupoid. Cf. field, module, ring group automorphism   A group isomorphism from a group to itself. That is, a bijective function from a group to itself that preserves the group operation, i.e. f(ab) = f(a)f(b) for all a, b. Cf. group homomorphism, group isomorphism. group homomorphism   A function from one group to another that preserves the group operation, i.e., f(ab) = f(a)f(b) for all a, b. Cf. group automorphism, group isomorphism. group isomorphism   A group homomorphism that is both “one-to-one” and “onto.” That is, a bijective function from one group to another that preserves the group operation, i.e. f(ab) = f(a)f(b) for all a, b. Cf. group homomorphism, group automorphism. groupoid   See group. harmonic series   The infinite series whose terms are the reciprocals of the natural numbers This series diverges, i.e., the sum does not exist. Related article: Series Hausdorff space   A topological space is Hausdorff if every pair of distinct points have disjoint neighborhoods. Two disjoint compact sets in a Hausdorff space have disjoint neighborhoods. A compact subset of a Hausdorff space is closed. Heawood Map Coloring Theorem   For every positive integer n, the chromatic number of the orientable surface of genus n (sphere with n handles) is given by For n = 0, this statement is exactly the Four Color Theorem, which was proven later, and does not bear Heawood's name. Heine-Borel property   Every closed and bounded subset of the real numbers is compact. Hempel’s Ravens Paradox    ARTICLE   A paradox of inductive logic described by the philosopher C.G. Hempel. See the article for a complete exposition.
		generalized continuum hypothesis – Hempel’s Ravens Paradox

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