Preceding implies Inclusion of Segments of Auxiliary Relation
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Theorem
Let $\left({S, \vee, \preceq}\right)$ be a bounded below join semilattice.
Let $R$ be an auxiliary relation on $S$.
Let $x, y \in S$ such that
- $x \preceq y$
Then
- $x^R \subseteq y^R$
where $x^R$ denotes the $R$-segment of $x$.
Proof
Let $a \in x^R$.
By definition of $R$-segment of $x$:
- $\left({a, x}\right) \in R$
By definition of reflexivity:
- $a \preceq a$
By definition of auxiliary relation:
- $\left({a, y}\right) \in R$
Thus by definition of $R$-segment of $y$:
- $a \in y^R$
$\blacksquare$
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_4:17