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Description: Function operation with the empty function. (Contributed by Thierry Arnoux, 27-May-2025)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | of0r | |- ( F oF R (/) ) = (/) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | df-of | |- oF R = ( f e. _V , g e. _V |-> ( x e. ( dom f i^i dom g ) |-> ( ( f ` x ) R ( g ` x ) ) ) ) |
|
| 2 | 1 | a1i | |- ( F e. _V -> oF R = ( f e. _V , g e. _V |-> ( x e. ( dom f i^i dom g ) |-> ( ( f ` x ) R ( g ` x ) ) ) ) ) |
| 3 | dmeq | |- ( f = F -> dom f = dom F ) |
|
| 4 | dmeq | |- ( g = (/) -> dom g = dom (/) ) |
|
| 5 | 3 4 | ineqan12d | |- ( ( f = F /\ g = (/) ) -> ( dom f i^i dom g ) = ( dom F i^i dom (/) ) ) |
| 6 | 5 | mpteq1d | |- ( ( f = F /\ g = (/) ) -> ( x e. ( dom f i^i dom g ) |-> ( ( f ` x ) R ( g ` x ) ) ) = ( x e. ( dom F i^i dom (/) ) |-> ( ( f ` x ) R ( g ` x ) ) ) ) |
| 7 | 6 | adantl | |- ( ( F e. _V /\ ( f = F /\ g = (/) ) ) -> ( x e. ( dom f i^i dom g ) |-> ( ( f ` x ) R ( g ` x ) ) ) = ( x e. ( dom F i^i dom (/) ) |-> ( ( f ` x ) R ( g ` x ) ) ) ) |
| 8 | dm0 | |- dom (/) = (/) |
|
| 9 | 8 | ineq2i | |- ( dom F i^i dom (/) ) = ( dom F i^i (/) ) |
| 10 | in0 | |- ( dom F i^i (/) ) = (/) |
|
| 11 | 9 10 | eqtri | |- ( dom F i^i dom (/) ) = (/) |
| 12 | 11 | a1i | |- ( ( F e. _V /\ ( f = F /\ g = (/) ) ) -> ( dom F i^i dom (/) ) = (/) ) |
| 13 | 12 | mpteq1d | |- ( ( F e. _V /\ ( f = F /\ g = (/) ) ) -> ( x e. ( dom F i^i dom (/) ) |-> ( ( f ` x ) R ( g ` x ) ) ) = ( x e. (/) |-> ( ( f ` x ) R ( g ` x ) ) ) ) |
| 14 | mpt0 | |- ( x e. (/) |-> ( ( f ` x ) R ( g ` x ) ) ) = (/) |
|
| 15 | 14 | a1i | |- ( ( F e. _V /\ ( f = F /\ g = (/) ) ) -> ( x e. (/) |-> ( ( f ` x ) R ( g ` x ) ) ) = (/) ) |
| 16 | 7 13 15 | 3eqtrd | |- ( ( F e. _V /\ ( f = F /\ g = (/) ) ) -> ( x e. ( dom f i^i dom g ) |-> ( ( f ` x ) R ( g ` x ) ) ) = (/) ) |
| 17 | id | |- ( F e. _V -> F e. _V ) |
|
| 18 | 0ex | |- (/) e. _V |
|
| 19 | 18 | a1i | |- ( F e. _V -> (/) e. _V ) |
| 20 | 2 16 17 19 19 | ovmpod | |- ( F e. _V -> ( F oF R (/) ) = (/) ) |
| 21 | 1 | reldmmpo | |- Rel dom oF R |
| 22 | 21 | ovprc1 | |- ( -. F e. _V -> ( F oF R (/) ) = (/) ) |
| 23 | 20 22 | pm2.61i | |- ( F oF R (/) ) = (/) |