| Step | Hyp | Ref | Expression | 
						
							| 1 |  | sbcimg | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝜑  →  ( 𝜓  →  𝜒 ) )  ↔  ( [ 𝐴  /  𝑥 ] 𝜑  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) ) ) ) | 
						
							| 2 | 1 | biimpd | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝜑  →  ( 𝜓  →  𝜒 ) )  →  ( [ 𝐴  /  𝑥 ] 𝜑  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) ) ) ) | 
						
							| 3 |  | sbcimg | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 )  ↔  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) | 
						
							| 4 |  | imbi2 | ⊢ ( ( [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 )  ↔  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  ( ( [ 𝐴  /  𝑥 ] 𝜑  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) )  ↔  ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) ) | 
						
							| 5 | 4 | biimpcd | ⊢ ( ( [ 𝐴  /  𝑥 ] 𝜑  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) )  →  ( ( [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 )  ↔  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) ) | 
						
							| 6 | 2 3 5 | syl6ci | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝜑  →  ( 𝜓  →  𝜒 ) )  →  ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) ) | 
						
							| 7 |  | idd | ⊢ ( 𝐴  ∈  𝑉  →  ( ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) ) | 
						
							| 8 |  | biimpr | ⊢ ( ( [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 )  ↔  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  ( ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 )  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) ) ) | 
						
							| 9 | 3 7 8 | ee13 | ⊢ ( 𝐴  ∈  𝑉  →  ( ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  ( [ 𝐴  /  𝑥 ] 𝜑  →  [ 𝐴  /  𝑥 ] ( 𝜓  →  𝜒 ) ) ) ) | 
						
							| 10 | 9 1 | sylibrd | ⊢ ( 𝐴  ∈  𝑉  →  ( ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) )  →  [ 𝐴  /  𝑥 ] ( 𝜑  →  ( 𝜓  →  𝜒 ) ) ) ) | 
						
							| 11 | 6 10 | impbid | ⊢ ( 𝐴  ∈  𝑉  →  ( [ 𝐴  /  𝑥 ] ( 𝜑  →  ( 𝜓  →  𝜒 ) )  ↔  ( [ 𝐴  /  𝑥 ] 𝜑  →  ( [ 𝐴  /  𝑥 ] 𝜓  →  [ 𝐴  /  𝑥 ] 𝜒 ) ) ) ) |