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lean4game/server/testgame/TestGame/Levels/SetTheory/L15_Powerset.lean

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import TestGame.Metadata
import Mathlib.Data.Set.Basic
import Mathlib.Algebra.Parity
import Mathlib.Tactic.Ring
import TestGame.ToBePorted
Game "TestGame"
World "SetTheory2"
Level 2
Title "Potenzmenge"
Introduction
"
Eine andere wichtige Menge ist die Potenzmenge einer Menge, welche als
`𝒫 A` geschrieben wird (`\\powerset`). Diese ist als `{S | S ⊆ A}` definiert, also
alle Mengen, die in $A$ enthalten sind.
Eines der wichtigsten Lemmas ist `mem_powerset_iff: x ∈ 𝒫 s ↔ x ⊆ s` welches
im Grunde die Definition einsetzt.
"
open Set
Statement
"" (X Y : Set ):
𝒫 X 𝒫 Y ⊆ 𝒫 (X Y) := by
intro A hA
rw [mem_union] at hA
simp_rw [mem_powerset_iff] at *
rcases hA with hA | hA
apply subset_union_of_subset_left
assumption
apply subset_union_of_subset_right
assumption
NewTactics constructor intro rw assumption rcases simp tauto trivial
NewLemmas Subset.antisymm_iff empty_subset