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For example: For all real numbers a and b, if a = b, then a ≥ 0 implies b ≥ 0 (here, () is x ≥ 0). This is a property which is most often used in algebra, especially in solving systems of equations, but is apllied in nearly every area of math that uses equality
For example: "An even number is an integer which is divisible by 2." An extensional definition instead lists all objects where the term applies. For example: "An even number is any one of the following integers: 0, 2, 4, 6, 8..., -2, -4, -8..." In logic, the extension of a predicate is the set of all things for which the predicate is true. [47]
Change of variables is an operation that is related to substitution. However these are different operations, as can be seen when considering differentiation or integration (integration by substitution). A very simple example of a useful variable change can be seen in the problem of finding the roots of the sixth-degree polynomial:
Computational real algebraic geometry is concerned with the algorithmic aspects of real algebraic (and semialgebraic) geometry. The main algorithm is cylindrical algebraic decomposition. It is used to cut semialgebraic sets into nice pieces and to compute their projections. Real algebra is the part of algebra which is relevant to real algebraic ...
By the uniqueness of the singular value decomposition, the vectors ^ are then unique up to a real, orthogonal or unitary transformation among them, and the vectors ^ and ^ ′ (and hence ^) are unique up to equal real, orthogonal or unitary transformations applied simultaneously to the sets of the vectors ^ associated with a common value of and ...
A cardinal invariant is a property of the real line measured by a cardinal number. For example, a well-studied invariant is the smallest cardinality of a collection of meagre sets of reals whose union is the entire real line. These are invariants in the sense that any two isomorphic models of set theory must give the same cardinal for each ...
Taking precautions to protect yourself from a quartet of infectious diseases can lessen your odds of starting off 2025 sick.
Substitution, written M[x := N], is the process of replacing all free occurrences of the variable x in the expression M with expression N. Substitution on terms of the lambda calculus is defined by recursion on the structure of terms, as follows (note: x and y are only variables while M and N are any lambda expression): x[x := N] = N