| Step | Hyp | Ref | Expression | 
						
							| 1 |  | tngbas.t | ⊢ 𝑇  =  ( 𝐺  toNrmGrp  𝑁 ) | 
						
							| 2 |  | tngds.2 | ⊢  −   =  ( -g ‘ 𝐺 ) | 
						
							| 3 |  | dsid | ⊢ dist  =  Slot  ( dist ‘ ndx ) | 
						
							| 4 |  | dsndxntsetndx | ⊢ ( dist ‘ ndx )  ≠  ( TopSet ‘ ndx ) | 
						
							| 5 | 3 4 | setsnid | ⊢ ( dist ‘ ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 ) )  =  ( dist ‘ ( ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 )  sSet  〈 ( TopSet ‘ ndx ) ,  ( MetOpen ‘ ( 𝑁  ∘   −  ) ) 〉 ) ) | 
						
							| 6 | 2 | fvexi | ⊢  −   ∈  V | 
						
							| 7 |  | coexg | ⊢ ( ( 𝑁  ∈  𝑉  ∧   −   ∈  V )  →  ( 𝑁  ∘   −  )  ∈  V ) | 
						
							| 8 | 6 7 | mpan2 | ⊢ ( 𝑁  ∈  𝑉  →  ( 𝑁  ∘   −  )  ∈  V ) | 
						
							| 9 | 3 | setsid | ⊢ ( ( 𝐺  ∈  V  ∧  ( 𝑁  ∘   −  )  ∈  V )  →  ( 𝑁  ∘   −  )  =  ( dist ‘ ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 ) ) ) | 
						
							| 10 | 8 9 | sylan2 | ⊢ ( ( 𝐺  ∈  V  ∧  𝑁  ∈  𝑉 )  →  ( 𝑁  ∘   −  )  =  ( dist ‘ ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 ) ) ) | 
						
							| 11 |  | eqid | ⊢ ( 𝑁  ∘   −  )  =  ( 𝑁  ∘   −  ) | 
						
							| 12 |  | eqid | ⊢ ( MetOpen ‘ ( 𝑁  ∘   −  ) )  =  ( MetOpen ‘ ( 𝑁  ∘   −  ) ) | 
						
							| 13 | 1 2 11 12 | tngval | ⊢ ( ( 𝐺  ∈  V  ∧  𝑁  ∈  𝑉 )  →  𝑇  =  ( ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 )  sSet  〈 ( TopSet ‘ ndx ) ,  ( MetOpen ‘ ( 𝑁  ∘   −  ) ) 〉 ) ) | 
						
							| 14 | 13 | fveq2d | ⊢ ( ( 𝐺  ∈  V  ∧  𝑁  ∈  𝑉 )  →  ( dist ‘ 𝑇 )  =  ( dist ‘ ( ( 𝐺  sSet  〈 ( dist ‘ ndx ) ,  ( 𝑁  ∘   −  ) 〉 )  sSet  〈 ( TopSet ‘ ndx ) ,  ( MetOpen ‘ ( 𝑁  ∘   −  ) ) 〉 ) ) ) | 
						
							| 15 | 5 10 14 | 3eqtr4a | ⊢ ( ( 𝐺  ∈  V  ∧  𝑁  ∈  𝑉 )  →  ( 𝑁  ∘   −  )  =  ( dist ‘ 𝑇 ) ) | 
						
							| 16 |  | co02 | ⊢ ( 𝑁  ∘  ∅ )  =  ∅ | 
						
							| 17 | 3 | str0 | ⊢ ∅  =  ( dist ‘ ∅ ) | 
						
							| 18 | 16 17 | eqtri | ⊢ ( 𝑁  ∘  ∅ )  =  ( dist ‘ ∅ ) | 
						
							| 19 |  | fvprc | ⊢ ( ¬  𝐺  ∈  V  →  ( -g ‘ 𝐺 )  =  ∅ ) | 
						
							| 20 | 2 19 | eqtrid | ⊢ ( ¬  𝐺  ∈  V  →   −   =  ∅ ) | 
						
							| 21 | 20 | coeq2d | ⊢ ( ¬  𝐺  ∈  V  →  ( 𝑁  ∘   −  )  =  ( 𝑁  ∘  ∅ ) ) | 
						
							| 22 |  | reldmtng | ⊢ Rel  dom   toNrmGrp | 
						
							| 23 | 22 | ovprc1 | ⊢ ( ¬  𝐺  ∈  V  →  ( 𝐺  toNrmGrp  𝑁 )  =  ∅ ) | 
						
							| 24 | 1 23 | eqtrid | ⊢ ( ¬  𝐺  ∈  V  →  𝑇  =  ∅ ) | 
						
							| 25 | 24 | fveq2d | ⊢ ( ¬  𝐺  ∈  V  →  ( dist ‘ 𝑇 )  =  ( dist ‘ ∅ ) ) | 
						
							| 26 | 18 21 25 | 3eqtr4a | ⊢ ( ¬  𝐺  ∈  V  →  ( 𝑁  ∘   −  )  =  ( dist ‘ 𝑇 ) ) | 
						
							| 27 | 26 | adantr | ⊢ ( ( ¬  𝐺  ∈  V  ∧  𝑁  ∈  𝑉 )  →  ( 𝑁  ∘   −  )  =  ( dist ‘ 𝑇 ) ) | 
						
							| 28 | 15 27 | pm2.61ian | ⊢ ( 𝑁  ∈  𝑉  →  ( 𝑁  ∘   −  )  =  ( dist ‘ 𝑇 ) ) |