Proof of Theorem tailuni
| Step | Hyp | Ref
| Expression |
| 1 | | tailuni.1 |
. . . . . 6
 |
| 2 | 1 | tailmap 15636 |
. . . . 5
 Dir
tail         |
| 3 | | frn 4569 |
. . . . . . 7
 tail       tail     |
| 4 | 3 | sseld 2619 |
. . . . . 6
 tail        tail      |
| 5 | | visset 2295 |
. . . . . . 7
 |
| 6 | 5 | elpw 3037 |
. . . . . 6

   |
| 7 | 4, 6 | syl6ib 229 |
. . . . 5
 tail        tail     |
| 8 | 2, 7 | syl 12 |
. . . 4
 Dir

tail     |
| 9 | 8 | r19.21aiv 2175 |
. . 3
 Dir

tail     |
| 10 | | unissb 3208 |
. . 3
 
tail  
tail     |
| 11 | 9, 10 | sylibr 217 |
. 2
 Dir
 tail    |
| 12 | 1 | tailini 15637 |
. . . . . 6
  Dir

 tail       |
| 13 | | fnfvelrn 4786 |
. . . . . . 7
  tail 
  tail     tail    |
| 14 | | ffn 4562 |
. . . . . . . 8
 tail       tail    |
| 15 | 2, 14 | syl 12 |
. . . . . . 7
 Dir
tail    |
| 16 | 13, 15 | sylan 497 |
. . . . . 6
  Dir
  tail     tail    |
| 17 | | fvex 4689 |
. . . . . . 7
 tail      |
| 18 | | eleq2 1958 |
. . . . . . . 8
  tail     
 tail        |
| 19 | | eleq1 1957 |
. . . . . . . 8
  tail      tail   tail     tail     |
| 20 | 18, 19 | anbi12d 690 |
. . . . . . 7
  tail       tail     tail      tail     tail      |
| 21 | 17, 20 | cla4ev 2371 |
. . . . . 6
   tail      tail     tail      tail     |
| 22 | 12, 16, 21 | syl11anc 524 |
. . . . 5
  Dir
   
tail     |
| 23 | | eluni 3180 |
. . . . 5

 tail     tail     |
| 24 | 22, 23 | sylibr 217 |
. . . 4
  Dir

 tail    |
| 25 | 24 | ex 402 |
. . 3
 Dir

 tail     |
| 26 | 25 | ssrdv 2622 |
. 2
 Dir
 tail    |
| 27 | 11, 26 | eqssd 2633 |
1
 Dir
 tail    |