Step |
Hyp |
Ref |
Expression |
1 |
|
ineq1 |
|- ( ( A \ B ) = C -> ( ( A \ B ) i^i B ) = ( C i^i B ) ) |
2 |
|
disjdifr |
|- ( ( A \ B ) i^i B ) = (/) |
3 |
1 2
|
eqtr3di |
|- ( ( A \ B ) = C -> ( C i^i B ) = (/) ) |
4 |
|
uneq1 |
|- ( ( A \ B ) = C -> ( ( A \ B ) u. B ) = ( C u. B ) ) |
5 |
|
undif1 |
|- ( ( A \ B ) u. B ) = ( A u. B ) |
6 |
4 5
|
eqtr3di |
|- ( ( A \ B ) = C -> ( C u. B ) = ( A u. B ) ) |
7 |
3 6
|
jca |
|- ( ( A \ B ) = C -> ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) ) |
8 |
|
simpl |
|- ( ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) -> ( C i^i B ) = (/) ) |
9 |
|
disj3 |
|- ( ( C i^i B ) = (/) <-> C = ( C \ B ) ) |
10 |
|
eqcom |
|- ( C = ( C \ B ) <-> ( C \ B ) = C ) |
11 |
9 10
|
bitri |
|- ( ( C i^i B ) = (/) <-> ( C \ B ) = C ) |
12 |
8 11
|
sylib |
|- ( ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) -> ( C \ B ) = C ) |
13 |
|
difeq1 |
|- ( ( C u. B ) = ( A u. B ) -> ( ( C u. B ) \ B ) = ( ( A u. B ) \ B ) ) |
14 |
|
difun2 |
|- ( ( C u. B ) \ B ) = ( C \ B ) |
15 |
|
difun2 |
|- ( ( A u. B ) \ B ) = ( A \ B ) |
16 |
13 14 15
|
3eqtr3g |
|- ( ( C u. B ) = ( A u. B ) -> ( C \ B ) = ( A \ B ) ) |
17 |
16
|
eqeq1d |
|- ( ( C u. B ) = ( A u. B ) -> ( ( C \ B ) = C <-> ( A \ B ) = C ) ) |
18 |
17
|
adantl |
|- ( ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) -> ( ( C \ B ) = C <-> ( A \ B ) = C ) ) |
19 |
12 18
|
mpbid |
|- ( ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) -> ( A \ B ) = C ) |
20 |
7 19
|
impbii |
|- ( ( A \ B ) = C <-> ( ( C i^i B ) = (/) /\ ( C u. B ) = ( A u. B ) ) ) |