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# Edit detail for SandBox Aldor Category Theory Basics revision 3 of 3

 1 2 3 Editor: page Time: 2007/11/22 20:42:56 GMT-8 Note: fix link

```changed:
-[SandBox Aldor Category Theory 2]
[SandBox Aldor Category Theory Categories]
```

Miscellaneous Logical helper functions

aldor
```#include "axiom"
#pile
define Domain:Category == with;
+++
+++  A set is often considered to be a collection with "no duplicate elements."
+++  Here we have a slightly different definition which is important to
+++  understand.  We define a Set to be an arbitrary collection together with
+++  an equivalence relation "=".  Soon this will be made into a mathematical
+++  category where the morphisms are "functions", by which we mean maps
+++  having the special property that a=a' implies f a = f a'.  This definition
+++  is more convenient both mathematically and computationally, but you need
+++  to keep in mind that a set may have duplicate elements.
+++
define Set:Category == Join(Domain, Printable) with {
=:(%,%) -> Boolean;
}
+++
+++  A Preorder is a collection with reflexive and transitive <=, but without
+++  necessarily being symmetric (x<=y and y<=x) implying x=y.  Since
+++  (x<=y and y<=x) is always an equivalence relation, our definition of
+++  "Set" is always satisfied in any case.
+++
define Preorder:Category == Set with {
<=: (%,%) -> Boolean;
>=: (%,%) -> Boolean;
< : (%,%) -> Boolean;
> : (%,%) -> Boolean;
default {
(x:%) =(y:%):Boolean == (x<=y) and (y<=x);
(x:%)>=(y:%):Boolean ==  y<=x;
(x:%)< (y:%):Boolean == (x<=y) and ~(x=y);
(x:%)> (y:%):Boolean == (x>=y) and ~(x=y)
}
}
define TotalOrder:Category == Preorder with {
min: (%,%) -> %;
max: (%,%) -> %;
min: Tuple % -> %;
max: Tuple % -> %;
default {
min(x:%,y:%):% == { x<=y => x; y };
max(x:%,y:%):% == { x<=y => y; x };
import from List %;
min(t:Tuple %):% == associativeProduct(%,min,[t]);
max(t:Tuple %):% == associativeProduct(%,max,[t]);
}
}
+++
+++  Countable is the category of collections for which every element in the
+++  collection can be produced.  This is done by the generator "elements"
+++  below.  Note that there is no guarantee that elements will not produce
+++  "duplicates."  In fact, a Countable may not be a Set, so duplicates may
+++  have no meaning.  Also, Countable is not guaranteed to terminate.
+++
define Countable:Category == with {
elements: () -> Generator %
}
--
--  I'm using an empty function elements() rather than a constant elements
--  to avoid some compiler problems.
--
+++
+++  CountablyFinite is the same as Countable except that termination is
+++  guaranteed.
+++
define CountablyFinite:Category == Countable with
+++
+++  A "Monoids" is the usual Monoid (we don't use Monoid to avoid clashing
+++  with axllib): a Set with an associative product (associative relative to
+++  the equivalence relation of the Set, of course) and a unit.
+++
define Monoids:Category == Set with {
*: (%,%)            -> %;
1:                     %;
^:(%,Integer) -> %;
monoidProduct:   Tuple %  -> %;  -- associative product
monoidProduct:   List  %  -> %;
default {
(x:%)^(i:Integer):% == {
i=0 => 1;
i<0 => error "Monoid negative powers are not defined.";
associativeProduct(%,*,x for j:Integer in 1..i)
};
monoidProduct(t:Tuple %):% == { import from List %; monoidProduct(t) }
monoidProduct(l:List %):% == {
import from NonNegativeInteger;
#l = 0 => 1;
associativeProduct(%,*,l);
}
}
}
+++
+++  Groups are Groups in the usual mathematical sense.  We use "Groups"
+++  rather than "Group" to avoid clashing with axllib.
+++
define Groups:Category == Monoids with  {
inv: % -> %
}
+++
+++  Printing is a whole area that I'm going to have a nice categorical
+++  solution for, but still it is convenient to have a low level Printable
+++  signature for debugging purposes.
+++
define Printable:Category == with {
coerce: %    -> OutputForm;
coerce: List % -> OutputForm;
coerce: Generator % -> OutputForm;
default {
(t:OutputForm)**(l:List %):OutputForm == {
import from Integer;
empty? l => t;
hconcat(coerce first l, hspace(1)\$OutputForm) ** rest l;
};
coerce(l:List %):OutputForm == empty() ** l;
coerce(g:Generator %):OutputForm == {
import from List %;
empty() ** [x for x in g];
}
}
}
+++
+++  This evaluates associative products.
+++
associativeProduct(T:Type,p:(T,T)->T,g:Generator T):T == {
l:List T == [t for t in g];
associativeProduct(T,p,l);
}
associativeProduct(T:Type,p:(T,T)->T,l:List T):T == {
if empty? l then error "Empty product.";
mb(t:T,l:List T):T == { empty? l => t; mb( p(t,first l), rest l) };
mb(first l,rest l)
}
+++
+++  Evaluates the logical "For all ..." construction
+++
forall?(g:Generator Boolean):Boolean == {
q:Boolean := true;
for x:Boolean in g repeat { if ~x then { q := false; break } }
q
}
+++
+++  Evaluates the logical "There exists ..." construction
+++
exists?(g:Generator Boolean):Boolean == {
q:Boolean := false;
for x:Boolean in g repeat { if x then { q := true; break } };
q
}
+++
+++  The category of "Maps".  There is no implication that a map is a
+++  function in the sense of x=x' => f x = f x'
+++
define MapCategory(Obj:Category,A:Obj,B:Obj):Category == with {
apply: (%,A) -> B;
hom:  (A->B) -> %;
}
+++
+++  One convenient implementation of MapCategory
+++
Map(Obj:Category,A:Obj,B:Obj):MapCategory(Obj,A,B) == add {
Rep ==> A->B;
apply(f:%,a:A):B == (rep f) a;
hom  (f:A->B):% == per f
}
+++
+++  This strange function turns any Type into an Aldor Category
+++
define Categorify(T:Type):Category == with {
value: T
}
+++
+++  The null function
+++
null(A:Type,B:Type):(A->B) == (a:A):B +-> error "Attempt to evaluate the null function."
+++
+++ A handy package for composition of morphisms.  "o" is meant to suggest morphism composition g "o" f, to be coded "g ** f".
+++
o(Obj:Category,A:Obj,B:Obj,C:Obj): with
**: (B->C,A->B) -> (A->C)
(g:B->C)**(f:A->B):(A->C) == (a:A):C +-> g f a```
aldor
```   Compiling FriCAS source code from file
/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/basics.as
using Aldor compiler and options
-O -Fasy -Fao -Flsp -lfricas -Mno-ALDOR_W_WillObsolete -DFriCAS -Y \$FRICAS/algebra -I \$FRICAS/algebra
Use the system command )set compiler args to change these
options.
The )library system command was not called after compilation.```

Test Funtions

aldor
```#include "axiom"
#pile
#library lbasics "basics.ao"
import from lbasics
S:Set == Integer add
P:Preorder == Integer add
TO:TotalOrder == Integer add
--CC:Countable == Integer add
--  import from Integer, Generator(Integer)
--  elements():Generator(Integer) == generator (1..10)
M:Monoids == Integer add
G:Groups == Fraction Integer add
MAPS:MapCategory(SetCategory,Integer,Float) == Map(SetCategory,Integer,Float) add
value:Integer == 1
Null(n:PositiveInteger):Float==null(PositiveInteger,Float)(n)
sincos(x:Expression Integer):Expression Integer ==
import from o(SetCategory,Expression Integer,Expression Integer,Expression Integer)
( ((a:Expression Integer):Expression Integer +-> sin(a)) **
((b:Expression Integer):Expression Integer +-> cos(b)) ) (x)```
aldor
```   Compiling FriCAS source code from file
/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/7819217643380372071-25px002.as
using Aldor compiler and options
-O -Fasy -Fao -Flsp -lfricas -Mno-ALDOR_W_WillObsolete -DFriCAS -Y \$FRICAS/algebra -I \$FRICAS/algebra
Use the system command )set compiler args to change these
options.
The )library system command was not called after compilation.```

fricas
```)show T
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
T is not the name of a known type constructor. If you want to see
information about any operations named T , issue
)display operations T ```
fricas
```)show S
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
S is not the name of a known type constructor. If you want to see
information about any operations named S , issue
)display operations S ```
fricas
```)show P
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
P is not the name of a known type constructor. If you want to see
information about any operations named P , issue
)display operations P ```
fricas
```)show TO
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
TO is not the name of a known type constructor. If you want to
see information about any operations named TO , issue
)display operations TO
--)show CC```
fricas
```)show MAPS
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
MAPS is not the name of a known type constructor. If you want to
see information about any operations named MAPS , issue
)display operations MAPS ```
fricas
```)show INTS
The )show system command is used to display information about types
or partial types. For example, )show Integer will show
information about Integer .
INTS is not the name of a known type constructor. If you want to
see information about any operations named INTS , issue
)display operations INTS```

fricas
```sincos(x::Expression Integer)
There are no exposed library operations named sincos but there is
one unexposed operation with that name. Use HyperDoc Browse or
issue
)display op sincos
Cannot find a definition or applicable library operation named
sincos with argument type(s)
Expression(Integer)
Perhaps you should use "@" to indicate the required return type,
or "\$" to specify which version of the function you need.```

fricas
```Null(1)
There are no library operations named Null
Use HyperDoc Browse or issue
)what op Null
to learn if there is any operation containing " Null " in its
name.
Cannot find a definition or applicable library operation named Null
with argument type(s)
PositiveInteger
Perhaps you should use "@" to indicate the required return type,
or "\$" to specify which version of the function you need.```

SandBox Aldor Category Theory Categories