| Step | Hyp | Ref | Expression | 
						
							| 1 |  | sbcal | ⊢ ( [ 𝐴  /  𝑥 ] ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑧 [ 𝐴  /  𝑥 ] ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 2 |  | sbcal | ⊢ ( [ 𝐴  /  𝑥 ] ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑦 [ 𝐴  /  𝑥 ] ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 3 |  | sbcim2g | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) )  ↔  ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑦  →  ( [ 𝐴  /  𝑥 ] 𝑦  ∈  𝑥  →  [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑥 ) ) ) ) | 
						
							| 4 |  | sbcg | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑦  ↔  𝑧  ∈  𝑦 ) ) | 
						
							| 5 |  | sbcel2gv | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] 𝑦  ∈  𝑥  ↔  𝑦  ∈  𝐴 ) ) | 
						
							| 6 |  | sbcel2gv | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑥  ↔  𝑧  ∈  𝐴 ) ) | 
						
							| 7 |  | imbi13 | ⊢ ( ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑦  ↔  𝑧  ∈  𝑦 )  →  ( ( [ 𝐴  /  𝑥 ] 𝑦  ∈  𝑥  ↔  𝑦  ∈  𝐴 )  →  ( ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑥  ↔  𝑧  ∈  𝐴 )  →  ( ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑦  →  ( [ 𝐴  /  𝑥 ] 𝑦  ∈  𝑥  →  [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑥 ) )  ↔  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) ) ) ) | 
						
							| 8 | 4 5 6 7 | syl3c | ⊢ ( 𝐴  ∈  𝑉  →  ( ( [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑦  →  ( [ 𝐴  /  𝑥 ] 𝑦  ∈  𝑥  →  [ 𝐴  /  𝑥 ] 𝑧  ∈  𝑥 ) )  ↔  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) ) | 
						
							| 9 | 3 8 | bitrd | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) )  ↔  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) ) | 
						
							| 10 |  | pm3.31 | ⊢ ( ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) )  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 11 |  | pm3.3 | ⊢ ( ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  →  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) ) ) | 
						
							| 12 | 10 11 | impbii | ⊢ ( ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) )  ↔  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 13 | 12 | sbcbii | ⊢ ( [ 𝐴  /  𝑥 ] ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝑥  →  𝑧  ∈  𝑥 ) )  ↔  [ 𝐴  /  𝑥 ] ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 14 |  | pm3.31 | ⊢ ( ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) )  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) | 
						
							| 15 |  | pm3.3 | ⊢ ( ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 )  →  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 16 | 14 15 | impbii | ⊢ ( ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) )  ↔  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) | 
						
							| 17 | 9 13 16 | 3bitr3g | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 18 | 17 | albidv | ⊢ ( 𝐴  ∈  𝑉  →  ( ∀ 𝑦 [ 𝐴  /  𝑥 ] ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 19 | 2 18 | bitrid | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 20 | 19 | albidv | ⊢ ( 𝐴  ∈  𝑉  →  ( ∀ 𝑧 [ 𝐴  /  𝑥 ] ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 21 | 1 20 | bitrid | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 )  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 22 |  | dftr2 | ⊢ ( Tr  𝑥  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 23 | 22 | sbcbii | ⊢ ( [ 𝐴  /  𝑥 ] Tr  𝑥  ↔  [ 𝐴  /  𝑥 ] ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝑥 )  →  𝑧  ∈  𝑥 ) ) | 
						
							| 24 |  | dftr2 | ⊢ ( Tr  𝐴  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) | 
						
							| 25 | 21 23 24 | 3bitr4g | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] Tr  𝑥  ↔  Tr  𝐴 ) ) |