Furthermore,
D(L(a), a, a, ..., a, 1,1) = D(L(a, a), a, ..., a, 1,1)
=L(D(a, ..., a, a, 1,1), a)
=L(D(a, a, ..., a, 1,1)),
then
D(L(a), a, ..., a, 1,1) = L(D(a, a, ..., a, 1,1)).
(34)
Combining (33) and (34), we get
L(D(1, a, ..., a, 1,1)) = L(D(a, a, ..., a, 1,1)),
and by using Proposition 1 (iv) we see that
D(a, a, ..., a, a, 1,1) ≤D(1, a, ..., a, 1,1) and
from Lemma 1, we deduce that
D(a, ..., a, 1,1) = D(1, a, ..., a, ..., a, 1,1)
=D(a, ..., a, a, 1,1,1).(35)
Therefore, (32) and (35) show that
δ(a) = D(a, a, ..., a, a, 1,1,1).(36)
According to the results (27), (32) and (36), we
get δ(a) = D(a, ..., a, 1) = D(a, ..., a, 1,1) =
D(a, ..., a, 1,1,1),∀a∈G.
Using the same method of proof, we arrive at the fol-
lowing conclusion
δ(a) = D(a, a, ..., a, 1) = D(a, a, ..., a, 1,1) =
D(a, a, ..., a, 1,1,1) = ... =D(a, 1,1, ..., 1),∀a∈
G.
To complete this demonstration, it is enough to show
that D(a, 1,1, ..., 1) = a.
From Theorem 2, since δ(1) = 1, we get
D(a, 1,1, ..., 1) = a,∀a∈G. This means that
δ(a) = a,∀a∈G. Thus, the theorem is proved..
Proposition 4. Considered Gbe a poset and 0its
least element. Let δbe the trace of D. Denote
F ixδ(G) = {a∈G:δ(a) = a}. Then,
(1) 0∈F ixδ(G).
(2) If a∈F ixδ(G)and b≤a, then b∈F ixδ(G).
(3) If Gis directed, then ∀b1, b2∈F ixδ(P),
∃k∈F ixδ(G):b1≤kand b2≤k.
Proof. (1) It is clear that since δ(0) = 0.
(2) Let a, b ∈G. Assume that a∈F ixδ(G)and
b≤a, then δ(a) = a. By using Theorem 1 (1), we
have
D(L(b), a, ..., a) = D(L(a, b), a, ..., a, a)
=L(D(a, ..., a), b)
=L(δ(a), b)
=L(a, b)
=L(b).
Since b∈L(b), it follows that b∈
D(L(b), a, ..., a, a).Hence, ∃t∈L(b)provided
that b=D(t, a, ..., a), by using Proposition 1 (iv)
and (i), we get
b=D(t, a, ..., a)≤D(b, a, ..., a)≤b, so
D(b, a, ..., a) = b. (37)
Again,
D(b, L(b), a, ..., a) = D(b, L(a, b), a, ..., a)
=L(D(b, a, ..., a), b)
=L(b, b)using (37)
=L(b).
Since b∈L(b), we get b∈D(b, L(b), a, ..., a).
Hence, there exists t∈L(b)such that b=
D(b, t, a, ..., a), by using Proposition 1 (iv) and (i),
we get
b=D(b, t, a, ..., a)≤D(b, b, a, a, ..., a, a)≤b, so
D(b, b, a, ..., a) = b. (38)
Also by using Theorem 1 (1), we have
D(b, b, L(b), a, a, a, ..., a) = D(b, b, L(a, b), a, ..., a)
=L(D(b, b, a, a, ..., a, a), b)
=L(b, b)by , using (38)
=L(b).
Since b∈L(b), we find b∈D(b, b, L(b), a, ..., a).
Hence, we can find an t∈L(b)which b=
D(b, b, t, a, ..., a), by using Proposition 1 (iv) and (i),
we get
b=D(b, b, t, a, ..., a)≤D(b, b, b, a, a, ..., a)≤b, so
D(b, b, b, a, ..., a) = b. (39)
From the results (37), (38) and (39), we ob-
tain D(b, a, ..., a) = D(b, b, a, a, ..., a) =
D(b, b, b, a, ..., a) = b,∀a, b ∈G.
With the same method, we arrive at
D(b, a, ..., a) = D(b, b, a, ..., a) =
D(b, b, b, a, ..., a) = ... =D(b, b, ..., b, b, a) = b,∀
b∈G. So
D(b, b, ..., b, a) = b. (40)
Moreover,
D(b, ..., b, b, L(b)) = D(b, ..., b, L(a, b))
=L(D(b, ..., b, a), b)
=L(b, b)by (40)
=L(b).
WSEAS TRANSACTIONS on MATHEMATICS
DOI: 10.37394/23206.2024.23.58
Latifa Bedda, Abdelkarim Boua