1. Introduction and Preliminaries
The theory of algebraically closed fields with given characteristic is complete which means that we can capture all such fields that meat this theory. In this research we will first define directed single graphs of 1-arity and the construction of such graphs by defining the components of these graphs. Hence we can after present the theory of these graphs in general. This theory has many axioms which will be presented. However, not all these axioms can give a complete theory. Thus we will give a characteristic sequence which capture the strongly minimal directed single graphs of 1-arity, and algebraically close fields are strongly minimal [
1,
2] and show the theory of this sequence is uncountably categorical in all uncountable cardinals
ans hence is complete via Łos-Vaught test.
We introduce now preliminaries that are needed in this research, ref. [
3] is the main source of these preliminaries and recommended for more details.
A sequence of parameters in the graph G is written as . We write as formula in the tuples and of vertices. If the formula is true in G then we write The cardinality of the graph G is denoted by . Let . Then is the language obtained by adding constant symbols to L for each element in F and is the set of all -sentences true in G. The notation stands for the set of positive integers.
Definition 1 (p. 117, [
4])
. Let be an L-structure and . Let . We say X is definable with parameters from A if and only if there is an L-formula and elements such that . Theorem 1 ([
5])
. The Łos-Vaught test state that a theory is complete if it is uncountably categorical for each uncountable cardinal κ and it has no finite model. Definition 2 (p. 1, [
6])
. An infinite definable set , where X is definable with parameters, is called minimal if every definable (with parameters) subset of X is either finite or cofinite. If is the formula that defines X, then is minimal. We say that X and are strongly minimal if is minimal in any elementary extension of . Theorem 2 (p. 211, [
3])
. Suppose T is a strongly minimal theory in a countable language. If and , with , then . Definition 3. A graph G is a mathematical structure consists of the ordered pair where V is a set of vertices and E is a relation symbol defined by .
If G is directed graph, then where the edge starts from u to v and we denote such a graph by .
In the above definition, note that v and u in the set E are not necessarily distinct. So loops are allowed which are vertices with an edge from the vertex to itself.
Definition 4. Let be a directed graph and let . We define the relation for to be the edges directed from the vertex v to vertex w where l is the number of edges starting from v and is the length of each path from v to w.
Definition 5. Let be a directed graph. Then is called a graph of l-arity and denoted by if the following holds:If then is called a graph of 1-arity and is satisfies the formula Definition 6. Let be a directed graph with 1-arity. Then is called a single graph if it satisfy the followingwe denote such a graph by . If such that v satisties the formulathen v is the zero vertex and denoted by . 2. Classification of Directed Single Graphs of 1-Arity
Definition 7. Let and . If there is such that then are connected. Let . If any two vertices of C are connected then we say that C is connected. A connected component of is maximal connected graph.
Lemma 1. Every connected component of is either
- 1.
a copy of ,
- 2.
a copy of ,
- 3.
a copy of .
Proof. Let
C be a finite connected component of
. Let
. Then
So
for all
. Let
r be the smallest number in
such that
for some
. If
,
as
is a directed single graph with 1-arity. So,
, contradicting that
r is the smallest such number. So
which means that
C contains a cycle of period
r. Since
is a directed single graph with 1-arity,
.
Now let
C be infinite connected component. Let
. Then we have
If
for some
, and
, then
C is finite by the previous argument. So all
are distinct for
and we will have two possibilities:
First, there is
such that
satisfies the formula
then
C is
, i.e.,
.
Second, choosing any
, such that
v satisfies the formula
and
w is unique. So we have
for each
and for any
,
is distinct from
unless
. So,
. □
Example 1. - 1.
Consider the structure where the vertices are and the edges defined regarding the relation < as follows: This formula guarantee there is exactly one edge going from to . This formula is also true in but not true in as there is always an element such that . We can consider and regarding the above formula as copies of the connected component in . From this example, we learned a mathematical property about , , and which is , are countable structure and is uncountable.
- 2.
Consider the structure , then we need to the formula above will be: We can consider regarding the above formula as copy of the connected component in .
- 3.
Consider the permutation On defined by It is defined by the formula This permutation can be considered as a copy of the connected component in . Now take another permutation on defined by It is also defined by the formula By looking to this formula defined on τ we can see we have two connected components of in . The permutations σ and τ are in the permutation group of but from the formulas above we know what is the algebraic structures of these two permutations.
Such methodology can be applied on many algebraic structures, for example and hence we can study the cyclic subgroups in .
- 4.
Ref. [7] Consider the structure where is the successor function defined on the natural numbers as . It can be defined by the formula We can consider regarding the above formula as copy of the connected component in .
Definition 8. Let . We define the characteristic sequence for to bea sequence of cardinals such that is the numbers of copies of , is the numbers of copies of , and is the number of copies of for . Proposition 1. Let and . If Then .
2.1. Axiomatization of the Theory of Directed Single Graphs of 1-Arity
Definition 9. For a sequence where each , we axiomatize the theory by the following:If is finite, thenIf is infinite, thenFor each , if is finite, thenFor each , if is infinite, thenIf and there is such that for all , and is infinite, thenFor each , Definition 10. We define the dominant component in to be the component for some such that the following holds:If the dominant component in is for some , then is with cyclic dominant component of length i. Otherwise, is with the infinite dominant component . Definition 11. We define to be the characteristic sequence for strongly minimal directed single graphs of 1-arity in the language .
Lemma 2. If is strongly minimal, then the characteristic sequence satisfies one of the following cases:
- Case 1:
There is only finitely many infinite dominant components, that is, is finite.
- Case 2:
If is with cyclic dominant component of length i for some , then is infinite, , , and is finite.
Proof. - Case 1:
Let
be the formula
As
is 1-arity,
is infinite which means that
defines an infinite subset of
. Now,
will be the formula
which is equivalent to the formula
So
defines the zero vertices
in
. As
is strongly minimal,
defines a finite set. Hence, there is only finitly many
in
. So there is only finitely many infinite dominant component.
- Case 2:
Suppose
is with cyclic dominant component of length
i for some
. Then
Let
be the formula
. Now,
and
. But
is a cyclic dominant component. So
and
Thus,
is infinite which means there is infinitely many cyclic component of length
i and
defines this infinite subset of
. Since
is strongly minimal,
defines a finite subset of
. Hence,
,
, and
is finite.
□
2.2. Models of the Theory of Strongly Minimal Directed Single Graphs of 1-Arity
Proposition 2. The theory of strongly minimal directed single graphs of 1-arity satisfies the following:
- 1.
If the dominant component is cyclic of length i for some then is totally categorical
- 2.
If the dominant component is infinite then is uncountably categorical
Proposition 3. The theory of strongly minimal directed single graphs of 1-arity is complete.
Proof. If
and
is finite for all
. So there is
such that if
then
. So,
satisfy the formula
This means that if
then
is finite. So the complement of this set is not empty as
is infinite. So there is at least on copy of
. Suppose
. Then,
will be
where
.
If
and
is finite for all
but
is infinite, then
will be
where
.
So from the above cases and from Proposition 2,
is uncountably categorical. Also from the axiomatization of
, any model of
satisfy the axiom
Hence, by by the Łos-Vaught test,
is complete.
□
3. Conclusions and Future Work
This research started with classifying and then introduced all the axioms of the theory of . Then we proved the conditions of for the strongly minimal and examined the theory and proved is complete. The importance of such theory of such graphs is that we can apply many mathematical structures on it where as algebraically closed fields narrowed only on field theory.For example, we can apply groups, permutation groups, and other mathematical sets with some relation such as ordering relation and the successor function.
The goal of this work is we will show in the future that these structures can be Zariski Geometry. Zariski axioms relate algebra to geometry by topologize strongly minimal structures. When this is done the work will even be extended to directed single graphs with
l-arity not only 1-arity and give the complete theory of such graphs so that we can extend the range of the mathematical structure that can be applied on these graphs. Again we will show that these structures are Zariski Geometry.
and
classified strongly minimal structures which are Zariski Geometry are only algebraically closed fields, vector spaces, affine spaces, and pure sets [
8] and algebraically closed field are on top of these classification. Thus this research is aiming to be extended in the future to find a wide range of mathematical structures which is not listed in
and
classification.