Step |
Hyp |
Ref |
Expression |
1 |
|
df-he |
|
2 |
|
19.21v |
|
3 |
2
|
bicomi |
|
4 |
3
|
albii |
|
5 |
|
alcom |
|
6 |
|
impexp |
|
7 |
6
|
bicomi |
|
8 |
7
|
albii |
|
9 |
|
19.23v |
|
10 |
8 9
|
bitri |
|
11 |
10
|
albii |
|
12 |
4 5 11
|
3bitri |
|
13 |
|
dfss2 |
|
14 |
|
vex |
|
15 |
|
opeq2 |
|
16 |
15
|
eleq1d |
|
17 |
|
df-br |
|
18 |
16 17
|
bitr4di |
|
19 |
18
|
anbi2d |
|
20 |
19
|
exbidv |
|
21 |
14 20
|
elab |
|
22 |
21
|
imbi1i |
|
23 |
22
|
albii |
|
24 |
13 23
|
bitr2i |
|
25 |
|
dfima3 |
|
26 |
25
|
eqcomi |
|
27 |
26
|
sseq1i |
|
28 |
24 27
|
bitri |
|
29 |
12 28
|
bitr2i |
|
30 |
1 29
|
bitri |
|