| Step | Hyp | Ref | Expression | 
						
							| 1 |  | oppgtmd.1 |  |-  O = ( oppG ` G ) | 
						
							| 2 |  | tmdmnd |  |-  ( G e. TopMnd -> G e. Mnd ) | 
						
							| 3 | 1 | oppgmnd |  |-  ( G e. Mnd -> O e. Mnd ) | 
						
							| 4 | 2 3 | syl |  |-  ( G e. TopMnd -> O e. Mnd ) | 
						
							| 5 |  | eqid |  |-  ( TopOpen ` G ) = ( TopOpen ` G ) | 
						
							| 6 |  | eqid |  |-  ( Base ` G ) = ( Base ` G ) | 
						
							| 7 | 5 6 | tmdtopon |  |-  ( G e. TopMnd -> ( TopOpen ` G ) e. ( TopOn ` ( Base ` G ) ) ) | 
						
							| 8 | 1 6 | oppgbas |  |-  ( Base ` G ) = ( Base ` O ) | 
						
							| 9 | 1 5 | oppgtopn |  |-  ( TopOpen ` G ) = ( TopOpen ` O ) | 
						
							| 10 | 8 9 | istps |  |-  ( O e. TopSp <-> ( TopOpen ` G ) e. ( TopOn ` ( Base ` G ) ) ) | 
						
							| 11 | 7 10 | sylibr |  |-  ( G e. TopMnd -> O e. TopSp ) | 
						
							| 12 |  | eqid |  |-  ( +g ` G ) = ( +g ` G ) | 
						
							| 13 |  | id |  |-  ( G e. TopMnd -> G e. TopMnd ) | 
						
							| 14 | 7 7 | cnmpt2nd |  |-  ( G e. TopMnd -> ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> y ) e. ( ( ( TopOpen ` G ) tX ( TopOpen ` G ) ) Cn ( TopOpen ` G ) ) ) | 
						
							| 15 | 7 7 | cnmpt1st |  |-  ( G e. TopMnd -> ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> x ) e. ( ( ( TopOpen ` G ) tX ( TopOpen ` G ) ) Cn ( TopOpen ` G ) ) ) | 
						
							| 16 | 5 12 13 7 7 14 15 | cnmpt2plusg |  |-  ( G e. TopMnd -> ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( y ( +g ` G ) x ) ) e. ( ( ( TopOpen ` G ) tX ( TopOpen ` G ) ) Cn ( TopOpen ` G ) ) ) | 
						
							| 17 |  | eqid |  |-  ( +g ` O ) = ( +g ` O ) | 
						
							| 18 |  | eqid |  |-  ( +f ` O ) = ( +f ` O ) | 
						
							| 19 | 8 17 18 | plusffval |  |-  ( +f ` O ) = ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( x ( +g ` O ) y ) ) | 
						
							| 20 | 12 1 17 | oppgplus |  |-  ( x ( +g ` O ) y ) = ( y ( +g ` G ) x ) | 
						
							| 21 | 6 6 20 | mpoeq123i |  |-  ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( x ( +g ` O ) y ) ) = ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( y ( +g ` G ) x ) ) | 
						
							| 22 | 19 21 | eqtr2i |  |-  ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( y ( +g ` G ) x ) ) = ( +f ` O ) | 
						
							| 23 | 22 9 | istmd |  |-  ( O e. TopMnd <-> ( O e. Mnd /\ O e. TopSp /\ ( x e. ( Base ` G ) , y e. ( Base ` G ) |-> ( y ( +g ` G ) x ) ) e. ( ( ( TopOpen ` G ) tX ( TopOpen ` G ) ) Cn ( TopOpen ` G ) ) ) ) | 
						
							| 24 | 4 11 16 23 | syl3anbrc |  |-  ( G e. TopMnd -> O e. TopMnd ) |