Equivalence of Definitions of Bottom of Lattice
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Theorem
Let $\struct {S, \vee, \wedge, \preceq}$ be a lattice.
Let $\bot$ be a bottom of $\struct {S, \vee, \wedge, \preceq}$.
The following definitions of the concept of Bottom in the context of Lattice Theory are equivalent:
Definition 1
Let $S$ admit a smallest element $\bot$.
Then $\bot$ is called the bottom of $S$.
Definition 2
Let $\vee$ have an identity element $\bot$.
Then $\bot$ is called the bottom of $S$.
Proof
By definition, $\bot$ is the smallest element of $S$ if and only if for all $a \in S$:
- $\bot \preceq a$
By Ordering in terms of Join, this is equivalent to:
- $a \vee \bot = a$
If this equality holds for all $a \in S$, then by definition $\bot$ is an identity for $\vee$.
The result follows.
$\blacksquare$