| Step | Hyp | Ref | Expression | 
						
							| 1 |  | bicom | ⊢ ( ( 𝜃  ↔  𝜏 )  ↔  ( 𝜏  ↔  𝜃 ) ) | 
						
							| 2 |  | imbi2 | ⊢ ( ( ( 𝜃  ↔  𝜏 )  ↔  ( 𝜏  ↔  𝜃 ) )  →  ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) )  ↔  ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜏  ↔  𝜃 ) ) ) ) | 
						
							| 3 | 2 | biimpcd | ⊢ ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) )  →  ( ( ( 𝜃  ↔  𝜏 )  ↔  ( 𝜏  ↔  𝜃 ) )  →  ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜏  ↔  𝜃 ) ) ) ) | 
						
							| 4 | 1 3 | mpi | ⊢ ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) )  →  ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜏  ↔  𝜃 ) ) ) | 
						
							| 5 | 4 | 3expd | ⊢ ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) )  →  ( 𝜑  →  ( 𝜓  →  ( 𝜒  →  ( 𝜏  ↔  𝜃 ) ) ) ) ) | 
						
							| 6 |  | 3impexp | ⊢ ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜏  ↔  𝜃 ) )  ↔  ( 𝜑  →  ( 𝜓  →  ( 𝜒  →  ( 𝜏  ↔  𝜃 ) ) ) ) ) | 
						
							| 7 | 6 | biimpri | ⊢ ( ( 𝜑  →  ( 𝜓  →  ( 𝜒  →  ( 𝜏  ↔  𝜃 ) ) ) )  →  ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜏  ↔  𝜃 ) ) ) | 
						
							| 8 | 7 1 | imbitrrdi | ⊢ ( ( 𝜑  →  ( 𝜓  →  ( 𝜒  →  ( 𝜏  ↔  𝜃 ) ) ) )  →  ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) ) ) | 
						
							| 9 | 5 8 | impbii | ⊢ ( ( ( 𝜑  ∧  𝜓  ∧  𝜒 )  →  ( 𝜃  ↔  𝜏 ) )  ↔  ( 𝜑  →  ( 𝜓  →  ( 𝜒  →  ( 𝜏  ↔  𝜃 ) ) ) ) ) |