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-rw-r--r--pages/functional-analysis-basics/the-fundamental-four/open-mapping-theorem.md30
1 files changed, 15 insertions, 15 deletions
diff --git a/pages/functional-analysis-basics/the-fundamental-four/open-mapping-theorem.md b/pages/functional-analysis-basics/the-fundamental-four/open-mapping-theorem.md
index 53da008..b191bb2 100644
--- a/pages/functional-analysis-basics/the-fundamental-four/open-mapping-theorem.md
+++ b/pages/functional-analysis-basics/the-fundamental-four/open-mapping-theorem.md
@@ -3,7 +3,6 @@ title: Open Mapping Theorem
parent: The Fundamental Four
grand_parent: Functional Analysis Basics
nav_order: 3
-# cspell:words surjective bijective
---
# {{ page.title }}
@@ -13,12 +12,10 @@ where $X$ and $Y$ are topological spaces,
is called *open* if the image under $T$ of each open set of $X$
is open in $Y$.
-{: .theorem-title }
-> {{ page.title }}
-> {: #{{ page.title | slugify }} }
->
-> A bounded linear operator between Banach spaces is open
-> if and only if it is surjective.
+{% theorem * Open Mapping Theorem %}
+A bounded linear operator between Banach spaces is open
+if and only if it is surjective.
+{% endtheorem %}
{% proof %}
Let $X$ and $Y$ be Banach spaces
@@ -91,19 +88,22 @@ Conversely, suppose that $T$ is open. TODO
---
-XXX injective
For a bijective mapping between topological spaces, to say that it is open,
is equivalent to saying that its inverse is continuous.
The inverse of a bijective linear map between normed spaces is automatically linear
and thus continuous if and only if it is bounded.
As a corollary to the {{ page.title }} we obtain the following:
-{: .corollary-title }
-> Bounded Inverse Theorem
-> {: #bounded-inverse-theorem }
->
-> If a bounded linear operator between Banach spaces is bijective,
-> then its inverse is bounded.
-XXX relax to injective
+{% corollary * Bounded Inverse Theorem %}
+If a bounded linear operator between Banach spaces is bijective,
+then its inverse is bounded.
+{% endcorollary %}
Also known as *Inverse Mapping Theorem*.
+
+{% corollary %}
+Let $T: X \to Y$ be a bounded linear operator between Banach spaces
+and suppose that $T$ is injective, so that the inverse $T^{-1} : R(T) \to X$
+is defined on the range of $T$.
+The linear operator $T^{-1}$ is bounded if and only if $R(T)$ is closed in $X$.
+{% endcorollary %}