Magnus–Moldavansky Method
In the mathematical subject of group theory, a one-relator group is a group given by a group presentation with a single defining relation. One-relator groups play an important role in geometric group theory by providing many explicit examples of finitely presented groups. Formal definition A one-relator group is a group ''G'' that admits a group presentation of the form where ''X'' is a set (in general possibly infinite), and where r\in F(X) is a freely and cyclically reduced word. If ''Y'' is the set of all letters x\in X that appear in ''r'' and X'=X\setminus Y then :G=\langle Y\mid r=1\, \rangle \ast F(X'). For that reason ''X'' in () is usually assumed to be finite where one-relator groups are discussed, in which case () can be rewritten more explicitly as where X=\ for some integer n\ge 1. Freiheitssatz Let ''G'' be a one-relator group given by presentation () above. Recall that ''r'' is a freely and cyclically reduced word in ''F''(''X''). Let y\in X be a lett ...
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Group Theory
In abstract algebra, group theory studies the algebraic structures known as group (mathematics), groups. The concept of a group is central to abstract algebra: other well-known algebraic structures, such as ring (mathematics), rings, field (mathematics), fields, and vector spaces, can all be seen as groups endowed with additional operation (mathematics), operations and axioms. Groups recur throughout mathematics, and the methods of group theory have influenced many parts of algebra. Linear algebraic groups and Lie groups are two branches of group theory that have experienced advances and have become subject areas in their own right. Various physical systems, such as crystals and the hydrogen atom, and Standard Model, three of the four known fundamental forces in the universe, may be modelled by symmetry groups. Thus group theory and the closely related representation theory have many important applications in physics, chemistry, and materials science. Group theory is also cen ...
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