Extension of Infima Preserving Mapping to Complete Lattice Preserves Infima
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Theorem
Let $L_1 = \struct {S_1, \preceq_1}$, $L_2 = \struct {S_2, \preceq_2}$ be ordered sets.
Let $L_3 = \struct {S_3, \preceq_3}$ be a complete lattice.
Suppose that.
- $L_2$ is an infima inheriting ordered subset of $L_3$.
Let $f: S_1 \to S_2$ be a mapping such that:
- $f$ preserves infima.
Then
$f: S_1 \to S_3$ preserves infima.
Proof
By definition of ordered subset:
- $S_2 \subseteq S_3$
Then define $g = f:S_1 \to S_3$
Let $X$ be a subset of $S_1$ such that
- $X$ admits a infimum in $L_1$.
Thus by definition of complete lattice:
- $g \sqbrk X$ admits a infimum in $L_3$.
By definition of mapping preserves infima:
- $f \sqbrk X$ admits a infimum in $L_2$ and $\map {\inf_{L_2} } {f \sqbrk X} = \map f {\map {\inf_{L_1} } X}$
Thus by definition of infima inheriting:
- $\map {\inf_{L_3} } {g \sqbrk X} = \map g {\inf_{L_1} } X$
$\blacksquare$
Sources
- Mizar article WAYBEL13:21