| Step | Hyp | Ref | Expression | 
						
							| 1 |  | ralxpxfr2d.a | ⊢ 𝐴  ∈  V | 
						
							| 2 |  | ralxpxfr2d.b | ⊢ ( 𝜑  →  ( 𝑥  ∈  𝐵  ↔  ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴 ) ) | 
						
							| 3 |  | ralxpxfr2d.c | ⊢ ( ( 𝜑  ∧  𝑥  =  𝐴 )  →  ( 𝜓  ↔  𝜒 ) ) | 
						
							| 4 |  | df-ral | ⊢ ( ∀ 𝑥  ∈  𝐵 𝜓  ↔  ∀ 𝑥 ( 𝑥  ∈  𝐵  →  𝜓 ) ) | 
						
							| 5 | 2 | imbi1d | ⊢ ( 𝜑  →  ( ( 𝑥  ∈  𝐵  →  𝜓 )  ↔  ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) ) | 
						
							| 6 | 5 | albidv | ⊢ ( 𝜑  →  ( ∀ 𝑥 ( 𝑥  ∈  𝐵  →  𝜓 )  ↔  ∀ 𝑥 ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) ) | 
						
							| 7 | 4 6 | bitrid | ⊢ ( 𝜑  →  ( ∀ 𝑥  ∈  𝐵 𝜓  ↔  ∀ 𝑥 ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) ) | 
						
							| 8 |  | ralcom4 | ⊢ ( ∀ 𝑦  ∈  𝐶 ∀ 𝑥 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑥 ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 9 |  | ralcom4 | ⊢ ( ∀ 𝑧  ∈  𝐷 ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑥 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 10 | 9 | ralbii | ⊢ ( ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑥 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 11 |  | r19.23v | ⊢ ( ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ( ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 12 | 11 | ralbii | ⊢ ( ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑦  ∈  𝐶 ( ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 13 |  | r19.23v | ⊢ ( ∀ 𝑦  ∈  𝐶 ( ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 )  ↔  ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 14 | 12 13 | bitr2i | ⊢ ( ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 15 | 14 | albii | ⊢ ( ∀ 𝑥 ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑥 ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 16 | 8 10 15 | 3bitr4ri | ⊢ ( ∀ 𝑥 ( ∃ 𝑦  ∈  𝐶 ∃ 𝑧  ∈  𝐷 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 ) ) | 
						
							| 17 | 7 16 | bitrdi | ⊢ ( 𝜑  →  ( ∀ 𝑥  ∈  𝐵 𝜓  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 ) ) ) | 
						
							| 18 | 3 | pm5.74da | ⊢ ( 𝜑  →  ( ( 𝑥  =  𝐴  →  𝜓 )  ↔  ( 𝑥  =  𝐴  →  𝜒 ) ) ) | 
						
							| 19 | 18 | albidv | ⊢ ( 𝜑  →  ( ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜒 ) ) ) | 
						
							| 20 |  | biidd | ⊢ ( 𝑥  =  𝐴  →  ( 𝜒  ↔  𝜒 ) ) | 
						
							| 21 | 1 20 | ceqsalv | ⊢ ( ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜒 )  ↔  𝜒 ) | 
						
							| 22 | 19 21 | bitrdi | ⊢ ( 𝜑  →  ( ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 )  ↔  𝜒 ) ) | 
						
							| 23 | 22 | 2ralbidv | ⊢ ( 𝜑  →  ( ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 ∀ 𝑥 ( 𝑥  =  𝐴  →  𝜓 )  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 𝜒 ) ) | 
						
							| 24 | 17 23 | bitrd | ⊢ ( 𝜑  →  ( ∀ 𝑥  ∈  𝐵 𝜓  ↔  ∀ 𝑦  ∈  𝐶 ∀ 𝑧  ∈  𝐷 𝜒 ) ) |