Von Neumann Boundedness #
This file defines natural or von Neumann bounded sets and proves elementary properties.
Main declarations #
Bornology.IsVonNBounded
: A sets
is von Neumann-bounded if every neighborhood of zero absorbss
.Bornology.vonNBornology
: The bornology made of the von Neumann-bounded sets.
Main results #
Bornology.IsVonNBounded.of_topologicalSpace_le
: A coarser topology admits more von Neumann-bounded sets.Bornology.IsVonNBounded.image
: A continuous linear image of a bounded set is bounded.Bornology.isVonNBounded_iff_smul_tendsto_zero
: Given any sequenceε
of scalars which tends to𝓝[≠] 0
, we have that a setS
is bounded if and only if for any sequencex : ℕ → S
,ε • x
tends to 0. This shows that bounded sets are completely determined by sequences, which is the key fact for proving that sequential continuity implies continuity for linear maps defined on a bornological space
References #
A set s
is von Neumann bounded if every neighborhood of 0 absorbs s
.
Instances For
Alias of Filter.HasBasis.isVonNBounded_iff
.
Subsets of bounded sets are bounded.
The union of two bounded sets is bounded.
Alias of the forward direction of Bornology.isVonNBounded_neg
.
If a topology t'
is coarser than t
, then any set s
that is bounded with respect to
t
is bounded with respect to t'
.
Alias of the forward direction of Bornology.isVonNBounded_iff_tendsto_smallSets_nhds
.
A continuous linear image of a bounded set is bounded.
Given any sequence ε
of scalars which tends to 𝓝[≠] 0
, we have that a set S
is bounded
if and only if for any sequence x : ℕ → S
, ε • x
tends to 0. This actually works for any
indexing type ι
, but in the special case ι = ℕ
we get the important fact that convergent
sequences fully characterize bounded sets.
If a set is von Neumann bounded with respect to a smaller field,
then it is also von Neumann bounded with respect to a larger field.
See also Bornology.IsVonNBounded.restrict_scalars
below.
Singletons are bounded.
Alias of the reverse direction of Bornology.isVonNBounded_insert
.
The union of all bounded set is the whole space.
The von Neumann bornology defined by the von Neumann bounded sets.
Note that this is not registered as an instance, in order to avoid diamonds with the metric bornology.
Equations
- Bornology.vonNBornology 𝕜 E = Bornology.ofBounded (setOf (Bornology.IsVonNBounded 𝕜)) ⋯ ⋯ ⋯ ⋯
Instances For
In a normed space, the von Neumann bornology (Bornology.vonNBornology
) is equal to the
metric bornology.