| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							cnvco | 
							⊢ ◡ ( 𝑅  ∘  𝑆 )  =  ( ◡ 𝑆  ∘  ◡ 𝑅 )  | 
						
						
							| 2 | 
							
								
							 | 
							cnvss | 
							⊢ ( ( 𝑅  ∘  𝑆 )  ⊆  𝑇  →  ◡ ( 𝑅  ∘  𝑆 )  ⊆  ◡ 𝑇 )  | 
						
						
							| 3 | 
							
								1 2
							 | 
							eqsstrrid | 
							⊢ ( ( 𝑅  ∘  𝑆 )  ⊆  𝑇  →  ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ 𝑇 )  | 
						
						
							| 4 | 
							
								
							 | 
							cnvco | 
							⊢ ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  =  ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  | 
						
						
							| 5 | 
							
								
							 | 
							cnvss | 
							⊢ ( ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ 𝑇  →  ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ ◡ 𝑇 )  | 
						
						
							| 6 | 
							
								
							 | 
							sseq1 | 
							⊢ ( ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  =  ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  →  ( ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ ◡ 𝑇  ↔  ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  ⊆  ◡ ◡ 𝑇 ) )  | 
						
						
							| 7 | 
							
								
							 | 
							dfrel2 | 
							⊢ ( Rel  𝑅  ↔  ◡ ◡ 𝑅  =  𝑅 )  | 
						
						
							| 8 | 
							
								7
							 | 
							biimpi | 
							⊢ ( Rel  𝑅  →  ◡ ◡ 𝑅  =  𝑅 )  | 
						
						
							| 9 | 
							
								8
							 | 
							3ad2ant1 | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ◡ ◡ 𝑅  =  𝑅 )  | 
						
						
							| 10 | 
							
								
							 | 
							dfrel2 | 
							⊢ ( Rel  𝑆  ↔  ◡ ◡ 𝑆  =  𝑆 )  | 
						
						
							| 11 | 
							
								10
							 | 
							biimpi | 
							⊢ ( Rel  𝑆  →  ◡ ◡ 𝑆  =  𝑆 )  | 
						
						
							| 12 | 
							
								11
							 | 
							3ad2ant2 | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ◡ ◡ 𝑆  =  𝑆 )  | 
						
						
							| 13 | 
							
								9 12
							 | 
							coeq12d | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  =  ( 𝑅  ∘  𝑆 ) )  | 
						
						
							| 14 | 
							
								
							 | 
							dfrel2 | 
							⊢ ( Rel  𝑇  ↔  ◡ ◡ 𝑇  =  𝑇 )  | 
						
						
							| 15 | 
							
								14
							 | 
							biimpi | 
							⊢ ( Rel  𝑇  →  ◡ ◡ 𝑇  =  𝑇 )  | 
						
						
							| 16 | 
							
								15
							 | 
							3ad2ant3 | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ◡ ◡ 𝑇  =  𝑇 )  | 
						
						
							| 17 | 
							
								13 16
							 | 
							sseq12d | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  ⊆  ◡ ◡ 𝑇  ↔  ( 𝑅  ∘  𝑆 )  ⊆  𝑇 ) )  | 
						
						
							| 18 | 
							
								17
							 | 
							biimpcd | 
							⊢ ( ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  ⊆  ◡ ◡ 𝑇  →  ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( 𝑅  ∘  𝑆 )  ⊆  𝑇 ) )  | 
						
						
							| 19 | 
							
								6 18
							 | 
							biimtrdi | 
							⊢ ( ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  =  ( ◡ ◡ 𝑅  ∘  ◡ ◡ 𝑆 )  →  ( ◡ ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ ◡ 𝑇  →  ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( 𝑅  ∘  𝑆 )  ⊆  𝑇 ) ) )  | 
						
						
							| 20 | 
							
								4 5 19
							 | 
							mpsyl | 
							⊢ ( ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ 𝑇  →  ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( 𝑅  ∘  𝑆 )  ⊆  𝑇 ) )  | 
						
						
							| 21 | 
							
								20
							 | 
							com12 | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ 𝑇  →  ( 𝑅  ∘  𝑆 )  ⊆  𝑇 ) )  | 
						
						
							| 22 | 
							
								3 21
							 | 
							impbid2 | 
							⊢ ( ( Rel  𝑅  ∧  Rel  𝑆  ∧  Rel  𝑇 )  →  ( ( 𝑅  ∘  𝑆 )  ⊆  𝑇  ↔  ( ◡ 𝑆  ∘  ◡ 𝑅 )  ⊆  ◡ 𝑇 ) )  |