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  2. Extended real number line - Wikipedia

    en.wikipedia.org/wiki/Extended_real_number_line

    With the arithmetic operations defined above, ¯ is not even a semigroup, let alone a group, a ring or a field as in the case of . However, it has several convenient properties: + (+) and (+) + are either equal or both undefined.

  3. Projectively extended real line - Wikipedia

    en.wikipedia.org/wiki/Projectively_extended_real...

    Collectively they form the group PGL(2, R). The projectivities which are their own inverses are called involutions. A hyperbolic involution has two fixed points. Two of these correspond to elementary, arithmetic operations on the real projective line: negation and reciprocation. Indeed, 0 and ∞ are fixed under negation, while 1 and −1 are ...

  4. Aleph number - Wikipedia

    en.wikipedia.org/wiki/Aleph_number

    The aleph numbers differ from the infinity (∞) commonly found in algebra and calculus, in that the alephs measure the sizes of sets, while infinity is commonly defined either as an extreme limit of the real number line (applied to a function or sequence that "diverges to infinity" or "increases without bound"), or as an extreme point of the ...

  5. Cardinal number - Wikipedia

    en.wikipedia.org/wiki/Cardinal_number

    We can define arithmetic operations on cardinal numbers that generalize the ordinary operations for natural numbers. It can be shown that for finite cardinals, these operations coincide with the usual operations for natural numbers. Furthermore, these operations share many properties with ordinary arithmetic.

  6. Riemann sphere - Wikipedia

    en.wikipedia.org/wiki/Riemann_sphere

    In mathematics, the Riemann sphere, named after Bernhard Riemann, [1] is a model of the extended complex plane (also called the closed complex plane): the complex plane plus one point at infinity. This extended plane represents the extended complex numbers, that is, the complex numbers plus a value for infinity.

  7. Hyperoperation - Wikipedia

    en.wikipedia.org/wiki/Hyperoperation

    In mathematics, the hyperoperation sequence [nb 1] is an infinite sequence of arithmetic operations (called hyperoperations in this context) [1] [11] [13] that starts with a unary operation (the successor function with n = 0). The sequence continues with the binary operations of addition (n = 1), multiplication (n = 2), and exponentiation (n = 3).

  8. Wheel theory - Wikipedia

    en.wikipedia.org/wiki/Wheel_theory

    A wheel is an algebraic structure (,,, +,, /), in which . is a set, and are elements of that set, + and are binary operations, / is a unary operation, and satisfying the following properties:

  9. Surreal number - Wikipedia

    en.wikipedia.org/wiki/Surreal_number

    A visualization of the surreal number tree. In mathematics, the surreal number system is a totally ordered proper class containing not only the real numbers but also infinite and infinitesimal numbers, respectively larger or smaller in absolute value than any positive real number.