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lim sup X n consists of elements of X which belong to X n for infinitely many n (see countably infinite). That is, x ∈ lim sup X n if and only if there exists a subsequence (X n k) of (X n) such that x ∈ X n k for all k. lim inf X n consists of elements of X which belong to X n for all except finitely many n (i.e., for cofinitely many n).
For (,) a measurable space, a sequence μ n is said to converge setwise to a limit μ if = ()for every set .. Typical arrow notations are and .. For example, as a consequence of the Riemann–Lebesgue lemma, the sequence μ n of measures on the interval [−1, 1] given by μ n (dx) = (1 + sin(nx))dx converges setwise to Lebesgue measure, but it does not converge in total variation.
The supremum (abbreviated sup; pl.: suprema) of a subset of a partially ordered set is the least element in that is greater than or equal to each element of , if such an element exists. [1] If the supremum of S {\displaystyle S} exists, it is unique, and if b is an upper bound of S {\displaystyle S} , then the supremum of S {\displaystyle S} is ...
Fatou's lemma remains true if its assumptions hold -almost everywhere.In other words, it is enough that there is a null set such that the values {()} are non-negative for every .
In these limits, the infinitesimal change is often denoted or .If () is differentiable at , (+) = ′ ().This is the definition of the derivative.All differentiation rules can also be reframed as rules involving limits.
Let f 1, f 2, ... denote a sequence of real-valued measurable functions defined on a measure space (S,Σ,μ).If there exists a Lebesgue-integrable function g on S which dominates the sequence in absolute value, meaning that |f n | ≤ g for all natural numbers n, then all f n as well as the limit inferior and the limit superior of the f n are integrable and
On the other hand, if X is the domain of a function f(x) and if the limit as n approaches infinity of f(x n) is L for every arbitrary sequence of points {x n} in X − x 0 which converges to x 0, then the limit of the function f(x) as x approaches x 0 is equal to L. [10] One such sequence would be {x 0 + 1/n}.
This may be seen as follows: define f n (x) = n for x in the interval (0, 1/n] and f n (x) = 0 otherwise. Any g which dominates the sequence must also dominate the pointwise supremum h = sup n f n .