| Step | Hyp | Ref | Expression | 
						
							| 1 |  | excxor | ⊢ ( ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ⊻  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  ↔  ( ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  ¬  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  ∨  ( ¬  dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) ) ) | 
						
							| 2 |  | coass | ⊢ ( ( ◡ 𝐹  ∘  𝐹 )  ∘  𝐺 )  =  ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) ) | 
						
							| 3 |  | f1ococnv1 | ⊢ ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  →  ( ◡ 𝐹  ∘  𝐹 )  =  (  I   ↾  𝐴 ) ) | 
						
							| 4 | 3 | coeq1d | ⊢ ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  →  ( ( ◡ 𝐹  ∘  𝐹 )  ∘  𝐺 )  =  ( (  I   ↾  𝐴 )  ∘  𝐺 ) ) | 
						
							| 5 |  | f1of | ⊢ ( 𝐺 : 𝐴 –1-1-onto→ 𝐴  →  𝐺 : 𝐴 ⟶ 𝐴 ) | 
						
							| 6 |  | fcoi2 | ⊢ ( 𝐺 : 𝐴 ⟶ 𝐴  →  ( (  I   ↾  𝐴 )  ∘  𝐺 )  =  𝐺 ) | 
						
							| 7 | 5 6 | syl | ⊢ ( 𝐺 : 𝐴 –1-1-onto→ 𝐴  →  ( (  I   ↾  𝐴 )  ∘  𝐺 )  =  𝐺 ) | 
						
							| 8 | 4 7 | sylan9eq | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( ◡ 𝐹  ∘  𝐹 )  ∘  𝐺 )  =  𝐺 ) | 
						
							| 9 | 2 8 | eqtr3id | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  =  𝐺 ) | 
						
							| 10 | 9 | difeq1d | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  ∖   I  )  =  ( 𝐺  ∖   I  ) ) | 
						
							| 11 | 10 | dmeqd | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  dom  ( ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  ∖   I  )  =  dom  ( 𝐺  ∖   I  ) ) | 
						
							| 12 | 11 | adantr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  ∖   I  )  =  dom  ( 𝐺  ∖   I  ) ) | 
						
							| 13 |  | mvdco | ⊢ dom  ( ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  ∖   I  )  ⊆  ( dom  ( ◡ 𝐹  ∖   I  )  ∪  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  ) ) | 
						
							| 14 |  | f1omvdcnv | ⊢ ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  →  dom  ( ◡ 𝐹  ∖   I  )  =  dom  ( 𝐹  ∖   I  ) ) | 
						
							| 15 | 14 | ad2antrr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ◡ 𝐹  ∖   I  )  =  dom  ( 𝐹  ∖   I  ) ) | 
						
							| 16 |  | simprl | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 ) | 
						
							| 17 | 15 16 | eqsstrd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ◡ 𝐹  ∖   I  )  ⊆  𝑋 ) | 
						
							| 18 |  | simprr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) | 
						
							| 19 | 17 18 | unssd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  ( dom  ( ◡ 𝐹  ∖   I  )  ∪  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  ) )  ⊆  𝑋 ) | 
						
							| 20 | 13 19 | sstrid | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( ◡ 𝐹  ∘  ( 𝐹  ∘  𝐺 ) )  ∖   I  )  ⊆  𝑋 ) | 
						
							| 21 | 12 20 | eqsstrrd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) | 
						
							| 22 | 21 | expr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 )  →  ( dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋  →  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 23 | 22 | con3d | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 )  →  ( ¬  dom  ( 𝐺  ∖   I  )  ⊆  𝑋  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 24 | 23 | expimpd | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  ¬  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 25 |  | coass | ⊢ ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  =  ( 𝐹  ∘  ( 𝐺  ∘  ◡ 𝐺 ) ) | 
						
							| 26 |  | f1ococnv2 | ⊢ ( 𝐺 : 𝐴 –1-1-onto→ 𝐴  →  ( 𝐺  ∘  ◡ 𝐺 )  =  (  I   ↾  𝐴 ) ) | 
						
							| 27 | 26 | coeq2d | ⊢ ( 𝐺 : 𝐴 –1-1-onto→ 𝐴  →  ( 𝐹  ∘  ( 𝐺  ∘  ◡ 𝐺 ) )  =  ( 𝐹  ∘  (  I   ↾  𝐴 ) ) ) | 
						
							| 28 |  | f1of | ⊢ ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  →  𝐹 : 𝐴 ⟶ 𝐴 ) | 
						
							| 29 |  | fcoi1 | ⊢ ( 𝐹 : 𝐴 ⟶ 𝐴  →  ( 𝐹  ∘  (  I   ↾  𝐴 ) )  =  𝐹 ) | 
						
							| 30 | 28 29 | syl | ⊢ ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  →  ( 𝐹  ∘  (  I   ↾  𝐴 ) )  =  𝐹 ) | 
						
							| 31 | 27 30 | sylan9eqr | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( 𝐹  ∘  ( 𝐺  ∘  ◡ 𝐺 ) )  =  𝐹 ) | 
						
							| 32 | 25 31 | eqtrid | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  =  𝐹 ) | 
						
							| 33 | 32 | difeq1d | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  ∖   I  )  =  ( 𝐹  ∖   I  ) ) | 
						
							| 34 | 33 | dmeqd | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  dom  ( ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  ∖   I  )  =  dom  ( 𝐹  ∖   I  ) ) | 
						
							| 35 | 34 | adantr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  ∖   I  )  =  dom  ( 𝐹  ∖   I  ) ) | 
						
							| 36 |  | mvdco | ⊢ dom  ( ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  ∖   I  )  ⊆  ( dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ∪  dom  ( ◡ 𝐺  ∖   I  ) ) | 
						
							| 37 |  | simprr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) | 
						
							| 38 |  | f1omvdcnv | ⊢ ( 𝐺 : 𝐴 –1-1-onto→ 𝐴  →  dom  ( ◡ 𝐺  ∖   I  )  =  dom  ( 𝐺  ∖   I  ) ) | 
						
							| 39 | 38 | ad2antlr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ◡ 𝐺  ∖   I  )  =  dom  ( 𝐺  ∖   I  ) ) | 
						
							| 40 |  | simprl | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) | 
						
							| 41 | 39 40 | eqsstrd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ◡ 𝐺  ∖   I  )  ⊆  𝑋 ) | 
						
							| 42 | 37 41 | unssd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  ( dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ∪  dom  ( ◡ 𝐺  ∖   I  ) )  ⊆  𝑋 ) | 
						
							| 43 | 36 42 | sstrid | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( ( ( 𝐹  ∘  𝐺 )  ∘  ◡ 𝐺 )  ∖   I  )  ⊆  𝑋 ) | 
						
							| 44 | 35 43 | eqsstrrd | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) )  →  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 ) | 
						
							| 45 | 44 | expr | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  →  ( dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋  →  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 46 | 45 | con3d | ⊢ ( ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  ∧  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  →  ( ¬  dom  ( 𝐹  ∖   I  )  ⊆  𝑋  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 47 | 46 | expimpd | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( dom  ( 𝐺  ∖   I  )  ⊆  𝑋  ∧  ¬  dom  ( 𝐹  ∖   I  )  ⊆  𝑋 )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 48 | 47 | ancomsd | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( ¬  dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 49 | 24 48 | jaod | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  ¬  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  ∨  ( ¬  dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ∧  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 50 | 1 49 | biimtrid | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴 )  →  ( ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ⊻  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) ) | 
						
							| 51 | 50 | 3impia | ⊢ ( ( 𝐹 : 𝐴 –1-1-onto→ 𝐴  ∧  𝐺 : 𝐴 –1-1-onto→ 𝐴  ∧  ( dom  ( 𝐹  ∖   I  )  ⊆  𝑋  ⊻  dom  ( 𝐺  ∖   I  )  ⊆  𝑋 ) )  →  ¬  dom  ( ( 𝐹  ∘  𝐺 )  ∖   I  )  ⊆  𝑋 ) |