Topology on extended non-negative reals #
Topology on ℝ≥0∞.
Note: this is different from the EMetricSpace topology. The EMetricSpace topology has
IsOpen {⊤}, while this topology doesn't have singleton elements.
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The set of finite ℝ≥0∞ numbers is homeomorphic to ℝ≥0.
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The set of finite ℝ≥0∞ numbers is homeomorphic to ℝ≥0.
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Characterization of neighborhoods for ℝ≥0∞ numbers. See also tendsto_order
for a version with strict inequalities.
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The sum over the complement of a finset tends to 0 when the finset grows to cover the whole
space. This does not need a summability assumption, as otherwise all sums are zero.
A sum of extended nonnegative reals which is finite can have only finitely many terms above any positive threshold.
Markov's inequality for Finset.card and tsum in ℝ≥0∞.
Summable non-negative functions have countable support
A series of non-negative real numbers converges to r in the sense of HasSum if and only if
the sequence of partial sum converges to r.
For f : ℕ → ℝ≥0, then ∑' k, f (k + i) tends to zero. This does not require a summability
assumption on f, as otherwise all sums are zero.
Finitely summable non-negative functions have countable support
A series of non-negative real numbers converges to r in the sense of HasSum if and only if
the sequence of partial sum converges to r.
If a sequence f with non-negative terms is dominated by a sequence g with summable
series and at least one term of f is strictly smaller than the corresponding term in g,
then the series of f is strictly smaller than the series of g.
In an emetric ball, the distance between points is everywhere finite
Each ball in an extended metric space gives us a metric space, as the edist is everywhere finite.
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- metricSpaceEMetricBall a r = EMetricSpace.toMetricSpace (_ : ∀ (x y : ↑(EMetric.ball a r)), edist ↑x ↑y ≠ ⊤)
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Yet another metric characterization of Cauchy sequences on integers. This one is often the most efficient.
For a bounded set s : Set ℝ, its EMetric.diam is equal to sSup s - sInf s reinterpreted as
ℝ≥0∞.
For a bounded set s : Set ℝ, its Metric.diam is equal to sSup s - sInf s.
If edist (f n) (f (n+1)) is bounded above by a function d : ℕ → ℝ≥0∞,
then the distance from f n to the limit is bounded by ∑'_{k=n}^∞ d k.
If edist (f n) (f (n+1)) is bounded above by a function d : ℕ → ℝ≥0∞,
then the distance from f 0 to the limit is bounded by ∑'_{k=0}^∞ d k.