As in [
11] we start with 0 on all the edges of
G. Then, in every step we will choose
and
and add some labels to all the edges of the chosen walk from
to
. To be more specific, we will add some element
a of the group to the labels of all the edges having an odd position on the walk (starting from
) and
to the labels of all the edges having even position. It is possible that some labels will be modified more than once, as the walk does not need to be a path. We will denote such situation with
if we label a shortest even walk and
if we label the shortest odd walk. Observe that putting
results in adding
a to the weighted degrees of both
and
, while
means adding
a to the weighted degree of
and
to the weighted degree of
. In both cases, the operation does not change the weighted degree of any other vertex of the walk. Note that if some component
of
G is not bipartite, then for any vertices
there exist both even and odd walks.
Proof. By Theorems 1 and 2 we can assume that G is disconnected. We are going to divide the vertices of G into triples and pairs. Namely, we will take one triple from each component (or part of a bipartite component) which has odd order and all the remaining vertices we will join into pairs, then using the partition of the group from Corollary 2 we will arrive distinct weighted degrees of vertices. For this process we need some notation. Let be the number of bipartite components of G with both color classes odd, with both classes even and with one class odd and one even. Let be the number of remaining components of odd order and —the number of remaining components of even order. The number of triples equals to . The remaining vertices form the pairs. Observe that by Corollary 1 we can assume that . Moreover by Lemma 1 we assume that t is even.
We start with the case what implies . Let if ( and ) and otherwise. Let . Note that , therefore the set can be partitioned into m triples and l pairs such that for and for by Corollary 2. Let for and let for . It is easy to observe that for a given element not belonging to any triple, we have for some j.
Let us start the labeling. For both vertices and labels, we are numbering the pairs and triples consecutively, in the same order as they appear in the labeling algorithm described below, every time using the lowest index that has not been used so far (independently for the lists of couples and triples).
Given any bipartite component
G with both color classes even, we divide the vertices of every color class into pairs
, putting
for every such pair. This gives as weighted degrees
and
. We proceed in a similar way in the case of all the non-bipartite components of even order, coupling the vertices of every such component in any way.
Note, that since we use Corollary 2, we still need to find a way to include 0 and as weighted degrees, in order to do that, we will consider now two cases on .
Case 1.
Note that in this case . If both color classes of a bipartite component are of odd order, then they both have at least 3 vertices. We choose three of them, denoted with , and , in one class and another three, , and , in another one.
Suppose first that
for some
i. Without loss of generality we can assume that
and
. Note that
. We apply
Observe that , , , , and . Taking we proceed with the remaining vertices of these components as in the case when both color classes are even.
If now
for some
j. Without loss of generality we can assume that
and
. We apply
Observe that , , , , and . We proceed with the remaining vertices of these components as in the case when both color classes are even.
In the rest of bipartite component with both odd color classes, we apply:
In the case of non-bipartite components of odd order, we choose three vertices. We apply
Finally for bipartite components of odd order we choose four vertices
,
,
and
(
belongs to the even color class and three other vertices to the odd one). We apply
We proceed with the remaining vertices of these components as in the case when both color classes are even.
The labeling defined above is -irregular. Indeed, for in the triple of vertices the weighted degrees are equal to , and and in the pair we have and .
Case 2. .
Note that by Corollary 1 , what implies that .
Assume first that
. Then
,
and moreover
for some
j by Corollary 2. Without loss of generality we can assume that
and it is still unused. Let
. For the case of the non-bipartite component of odd order we choose three vertices
from the odd color class. For of such a component let
be two vertices from the even class. We apply
Observe that , , , , . We proceed with the remaining vertices of these components as in the case when both color classes are even.
If now
, then
and
for some
i by Corollary 2. Without loss of generality we can assume that
and
. We apply
Observe that , , , , . We proceed with the remaining vertices of these components as in the case when both color classes are even.
For all the remaining components we proceed the same as in Case 1.
For there is . If , then and and . For , then and . If , then and and . For let and for n even and and otherwise. We proceed in the same way as above (but not using the element ). □
By Theorem 2 and Lemma 2 we obtain immediately the following.