| Step | Hyp | Ref | Expression | 
						
							| 1 |  | axpownd | ⊢ ( ¬  𝑥  =  𝑦  →  ∃ 𝑥 ∀ 𝑦 ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 2 |  | df-ex | ⊢ ( ∃ 𝑧 𝑥  ∈  𝑦  ↔  ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦 ) | 
						
							| 3 | 2 | imbi1i | ⊢ ( ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  ↔  ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 ) ) | 
						
							| 4 | 3 | albii | ⊢ ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  ↔  ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 ) ) | 
						
							| 5 | 4 | imbi1i | ⊢ ( ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  ↔  ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 6 | 5 | albii | ⊢ ( ∀ 𝑦 ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  ↔  ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 7 | 6 | exbii | ⊢ ( ∃ 𝑥 ∀ 𝑦 ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  ↔  ∃ 𝑥 ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 8 |  | df-ex | ⊢ ( ∃ 𝑥 ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  ↔  ¬  ∀ 𝑥 ¬  ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 9 | 7 8 | bitri | ⊢ ( ∃ 𝑥 ∀ 𝑦 ( ∀ 𝑥 ( ∃ 𝑧 𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  ↔  ¬  ∀ 𝑥 ¬  ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 10 | 1 9 | sylib | ⊢ ( ¬  𝑥  =  𝑦  →  ¬  ∀ 𝑥 ¬  ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 ) ) | 
						
							| 11 | 10 | con4i | ⊢ ( ∀ 𝑥 ¬  ∀ 𝑦 ( ∀ 𝑥 ( ¬  ∀ 𝑧 ¬  𝑥  ∈  𝑦  →  ∀ 𝑦 𝑥  ∈  𝑧 )  →  𝑦  ∈  𝑥 )  →  𝑥  =  𝑦 ) |