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gradual-typing
sgdt
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13891ff8
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13891ff8
authored
7 years ago
by
Max New
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threeorders don't work
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freyd-multicategories.tex
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@@ -220,41 +220,70 @@ categories to get preorderd Freyd (multi)categories.
%
Further, we will likely (for the models' sake) need to develop
``double'' freyd multicategories as well.
%
To get that, we can use categories
\emph
{
internal
}
to Mono-categories.
\begin{definition}
[Double Mono-Category]
A double Mono Category is a category internal to the category of
Mono categories.
I've had several false starts here.
%
Here's 2 options that are
\emph
{
close
}
, but no cigar.
I
\emph
{
conjecture
}
that it is equivalent to a double category of
``loose'' vertical and horizontal arrows, and a sub-double-category
with the same objects.
\end{definition}
First, in analogy with double categories, we could just take
categories internal to Mono-categories, so a span of mono-categories
with identity and unit.
%
However, a span of Mono-categories is not quite right.
%
You have an object mono-category, representing objects and vertical
morphisms, but then your arrows are also a mono-category, so you have
only a
\emph
{
set
}
of arrows, and tight and loose
\emph
{
squares
}
and
source and target take tight squares to tight vertical morphisms.
%
So this is definitely not right
To get a preordered Mono category, there are two places to modify the
definition: at Mono, or at category internal to.
Second, instead of looking at
$
\Set
^{
\to
}$
and its refinement to Mono,
we could start with
$
\text
{
Preorder
}^{
\to
}$
or
$
\text
{
Cat
}^{
\to
}$
and
refine those somehow.
%
To get the right double category structure for the multicategory
stuff, this is the right order:
I think something here
\emph
{
includes
}
our categories, but is also too
big. Need to look into this more.
\begin{definition}
[Threeorder/3-Valued Preorder/Inclusion of Preorders]
A 3-valued Preorder or inclusion of preorders is a category enriched
in the ordinal 3:
$
0
\leq
1
\leq
2
$
, which is a reflective
subcategory of
$
\text
{
Set
}^{
\to
}$
defined by taking a set
$
X
$
to the
truth value
$
\exists
x
\in
X.
\top
$
.
%% To get that, we can use categories \emph{internal} to Mono-categories.
They are equivalent to an object with a ``tight'' and ``loose''
ordering, where tight ordering implies loose ordering.
\end{definition}
%% \begin{definition}[Double Mono-Category]
%% A double Mono Category is a category internal to the category of
%% Mono categories.
\begin{definition}
[Threeorder Category/Wide Double Subcategory]
A threeorder category is a category internal to threeorders.
%% I \emph{conjecture} that it is equivalent to a double category of
%% ``loose'' vertical and horizontal arrows, and a sub-double-category
%% with the same objects.
%% \end{definition}
It is equivalent (I think) to a pair of preorder category structures
on the same set of objects, where the preorder structures form a
threeorder, and the category structures form a Mono category.
\end{definition}
%% To get a preordered Mono category, there are two places to modify the
%% definition: at Mono, or at category internal to.
%% %
%% To get the right double category structure for the multicategory
%% stuff, this is the right order:
%% \begin{definition}[Threeorder/3-Valued Preorder/Inclusion of Preorders]
%% A 3-valued Preorder or inclusion of preorders is a category enriched
%% in the ordinal 3: $0 \leq 1 \leq 2$, which is a reflective
%% subcategory of $\text{Set}^{\to}$ defined by taking a set $X$ to the
%% truth value $\exists x\in X. \top$.
%% They are equivalent to an object with a ``tight'' and ``loose''
%% ordering, where tight ordering implies loose ordering.
%% \end{definition}
%% \begin{definition}[Threeorder Category/Wide Double Subcategory]
%% A threeorder category is a category internal to threeorders.
%% It is equivalent (I think) to a pair of preorder category structures
%% on the same set of objects, where the preorder structures form a
%% threeorder, and the category structures form a Mono category.
%% \end{definition}
\subsection
{
Kleisli Construction
}
Basically, take Coreflection(Kl(C,T))
\end{document}
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