Preceding is Auxiliary Relation
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Theorem
Let $\left({S, \vee, \preceq}\right)$ be a bounded below join semilattice.
Then
- $\preceq$ is an auxiliary relation.
Proof
- $\forall x, y \in S: x \preceq y \implies x \preceq y$
Then condition $(1)$ of auxiliary relation is satisfied.
By definition of transitivity:
- $\forall x, y, z, u \in S: x \preceq y \preceq z \preceq u \implies x \preceq u$
Then the condition $(2)$ of auxiliary relation is satisfied.
By definition of supremum:
- $\forall x, y, z \in S: x \preceq z \land y \preceq z \implies x \vee y \preceq z$
Then the condition $(3)$ of auxiliary relation is satisfied.
By definition of smallest element:
- $\forall x \in S: \bot \preceq x$
Then the condition $(4)$ of auxiliary relation is satisfied.
Thus the result by definition auxiliary relation.
$\blacksquare$
Sources
- 1980: G. Gierz, K.H. Hofmann, K. Keimel, J.D. Lawson, M.W. Mislove and D.S. Scott: A Compendium of Continuous Lattices
- Mizar article WAYBEL_4:funcreg 4