Subset is Compatible with Ordinal Addition
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Theorem
Let $x, y, z$ be ordinals.
Then:
- $(1): \quad x \le y \implies \paren {z + x} \le \paren {z + y}$
- $(2): \quad x \le y \implies \paren {x + z} \le \paren {y + z}$
Proof
The result follows from Subset is Left Compatible with Ordinal Addition and Subset is Right Compatible with Ordinal Addition.
$\blacksquare$