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Description: Value of the opposite functor. (Contributed by Zhi Wang, 13-Nov-2025)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | oppfvalg | |- ( ( F e. _V /\ G e. _V ) -> ( F oppFunc G ) = if ( ( Rel G /\ Rel dom G ) , <. F , tpos G >. , (/) ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | simpr | |- ( ( f = F /\ g = G ) -> g = G ) |
|
| 2 | 1 | releqd | |- ( ( f = F /\ g = G ) -> ( Rel g <-> Rel G ) ) |
| 3 | 1 | dmeqd | |- ( ( f = F /\ g = G ) -> dom g = dom G ) |
| 4 | 3 | releqd | |- ( ( f = F /\ g = G ) -> ( Rel dom g <-> Rel dom G ) ) |
| 5 | 2 4 | anbi12d | |- ( ( f = F /\ g = G ) -> ( ( Rel g /\ Rel dom g ) <-> ( Rel G /\ Rel dom G ) ) ) |
| 6 | simpl | |- ( ( f = F /\ g = G ) -> f = F ) |
|
| 7 | 1 | tposeqd | |- ( ( f = F /\ g = G ) -> tpos g = tpos G ) |
| 8 | 6 7 | opeq12d | |- ( ( f = F /\ g = G ) -> <. f , tpos g >. = <. F , tpos G >. ) |
| 9 | 5 8 | ifbieq1d | |- ( ( f = F /\ g = G ) -> if ( ( Rel g /\ Rel dom g ) , <. f , tpos g >. , (/) ) = if ( ( Rel G /\ Rel dom G ) , <. F , tpos G >. , (/) ) ) |
| 10 | df-oppf | |- oppFunc = ( f e. _V , g e. _V |-> if ( ( Rel g /\ Rel dom g ) , <. f , tpos g >. , (/) ) ) |
|
| 11 | opex | |- <. F , tpos G >. e. _V |
|
| 12 | 0ex | |- (/) e. _V |
|
| 13 | 11 12 | ifex | |- if ( ( Rel G /\ Rel dom G ) , <. F , tpos G >. , (/) ) e. _V |
| 14 | 9 10 13 | ovmpoa | |- ( ( F e. _V /\ G e. _V ) -> ( F oppFunc G ) = if ( ( Rel G /\ Rel dom G ) , <. F , tpos G >. , (/) ) ) |