| Step | Hyp | Ref
| Expression |
| 1 | | ccatcl 11049 |
. . . . 5
  Word
Word   ++  Word   |
| 2 | | lencl 10998 |
. . . . . . 7
 Word ♯    |
| 3 | 2 | nn0zd 9493 |
. . . . . 6
 Word ♯    |
| 4 | 3 | adantr 276 |
. . . . 5
  Word
Word  ♯    |
| 5 | 2 | adantr 276 |
. . . . . . 7
  Word
Word  ♯    |
| 6 | | lencl 10998 |
. . . . . . . 8
 Word ♯    |
| 7 | 6 | adantl 277 |
. . . . . . 7
  Word
Word  ♯    |
| 8 | 5, 7 | nn0addcld 9352 |
. . . . . 6
  Word
Word   ♯  ♯     |
| 9 | 8 | nn0zd 9493 |
. . . . 5
  Word
Word   ♯  ♯     |
| 10 | | swrdclg 11103 |
. . . . 5
   ++  Word ♯   ♯  ♯      ++  substr  ♯    ♯  ♯     Word   |
| 11 | 1, 4, 9, 10 | syl3anc 1250 |
. . . 4
  Word
Word    ++  substr  ♯    ♯  ♯     Word   |
| 12 | | wrdfn 11009 |
. . . 4
   ++  substr  ♯    ♯  ♯     Word
  ++  substr  ♯    ♯  ♯      ..^ ♯   ++  substr  ♯    ♯  ♯         |
| 13 | 11, 12 | syl 14 |
. . 3
  Word
Word    ++  substr  ♯    ♯  ♯      ..^ ♯   ++  substr  ♯    ♯  ♯         |
| 14 | | nn0uz 9683 |
. . . . . . . . . 10
     |
| 15 | 2, 14 | eleqtrdi 2298 |
. . . . . . . . 9
 Word ♯        |
| 16 | 15 | adantr 276 |
. . . . . . . 8
  Word
Word  ♯        |
| 17 | 3 | uzidd 9663 |
. . . . . . . . 9
 Word ♯     ♯     |
| 18 | | uzaddcl 9707 |
. . . . . . . . 9
  ♯     ♯   ♯    ♯  ♯      ♯     |
| 19 | 17, 6, 18 | syl2an 289 |
. . . . . . . 8
  Word
Word   ♯  ♯      ♯     |
| 20 | | elfzuzb 10141 |
. . . . . . . 8
 ♯      ♯  ♯     ♯       ♯  ♯      ♯      |
| 21 | 16, 19, 20 | sylanbrc 417 |
. . . . . . 7
  Word
Word  ♯      ♯  ♯      |
| 22 | | nn0addcl 9330 |
. . . . . . . . . . 11
  ♯  ♯    ♯  ♯     |
| 23 | 2, 6, 22 | syl2an 289 |
. . . . . . . . . 10
  Word
Word   ♯  ♯     |
| 24 | 23, 14 | eleqtrdi 2298 |
. . . . . . . . 9
  Word
Word   ♯  ♯         |
| 25 | 23 | nn0zd 9493 |
. . . . . . . . . 10
  Word
Word   ♯  ♯     |
| 26 | 25 | uzidd 9663 |
. . . . . . . . 9
  Word
Word   ♯  ♯       ♯  ♯      |
| 27 | | elfzuzb 10141 |
. . . . . . . . 9
  ♯  ♯       ♯  ♯   
  ♯  ♯        ♯  ♯       ♯  ♯       |
| 28 | 24, 26, 27 | sylanbrc 417 |
. . . . . . . 8
  Word
Word   ♯  ♯       ♯  ♯      |
| 29 | | ccatlen 11051 |
. . . . . . . . 9
  Word
Word  ♯  ++    ♯  ♯     |
| 30 | 29 | oveq2d 5960 |
. . . . . . . 8
  Word
Word     ♯  ++        ♯  ♯      |
| 31 | 28, 30 | eleqtrrd 2285 |
. . . . . . 7
  Word
Word   ♯  ♯      ♯  ++      |
| 32 | | swrdlen 11105 |
. . . . . . 7
   ++  Word ♯      ♯  ♯     ♯  ♯      ♯  ++    
♯   ++  substr  ♯    ♯  ♯        ♯  ♯   ♯     |
| 33 | 1, 21, 31, 32 | syl3anc 1250 |
. . . . . 6
  Word
Word  ♯   ++  substr  ♯    ♯  ♯        ♯  ♯   ♯     |
| 34 | 2 | nn0cnd 9350 |
. . . . . . 7
 Word ♯    |
| 35 | 6 | nn0cnd 9350 |
. . . . . . 7
 Word ♯    |
| 36 | | pncan2 8279 |
. . . . . . 7
  ♯  ♯     ♯  ♯   ♯   ♯    |
| 37 | 34, 35, 36 | syl2an 289 |
. . . . . 6
  Word
Word    ♯  ♯   ♯   ♯    |
| 38 | 33, 37 | eqtrd 2238 |
. . . . 5
  Word
Word  ♯   ++  substr  ♯    ♯  ♯      ♯    |
| 39 | 38 | oveq2d 5960 |
. . . 4
  Word
Word   ..^ ♯   ++  substr  ♯    ♯  ♯        ..^ ♯     |
| 40 | 39 | fneq2d 5365 |
. . 3
  Word
Word     ++  substr  ♯    ♯  ♯      ..^ ♯   ++  substr  ♯    ♯  ♯         ++  substr  ♯    ♯  ♯      ..^ ♯      |
| 41 | 13, 40 | mpbid 147 |
. 2
  Word
Word    ++  substr  ♯    ♯  ♯      ..^ ♯     |
| 42 | | wrdfn 11009 |
. . 3
 Word  ..^ ♯     |
| 43 | 42 | adantl 277 |
. 2
  Word
Word   ..^ ♯     |
| 44 | 1, 21, 31 | 3jca 1180 |
. . . 4
  Word
Word    ++  Word
♯      ♯  ♯     ♯  ♯      ♯  ++       |
| 45 | 37 | oveq2d 5960 |
. . . . . 6
  Word
Word   ..^  ♯  ♯   ♯     ..^ ♯     |
| 46 | 45 | eleq2d 2275 |
. . . . 5
  Word
Word    ..^  ♯  ♯   ♯     ..^ ♯      |
| 47 | 46 | biimpar 297 |
. . . 4
   Word
Word   ..^ ♯     ..^  ♯  ♯   ♯      |
| 48 | | swrdfv 11106 |
. . . 4
    ++  Word
♯      ♯  ♯     ♯  ♯      ♯  ++      ..^  ♯  ♯   ♯        ++  substr  ♯    ♯  ♯          ++     ♯      |
| 49 | 44, 47, 48 | syl2an2r 595 |
. . 3
   Word
Word   ..^ ♯       ++  substr  ♯    ♯  ♯          ++     ♯      |
| 50 | | ccatval3 11055 |
. . . 4
  Word
Word  ..^ ♯      ++     ♯          |
| 51 | 50 | 3expa 1206 |
. . 3
   Word
Word   ..^ ♯      ++     ♯          |
| 52 | 49, 51 | eqtrd 2238 |
. 2
   Word
Word   ..^ ♯       ++  substr  ♯    ♯  ♯              |
| 53 | 41, 43, 52 | eqfnfvd 5680 |
1
  Word
Word    ++  substr  ♯    ♯  ♯       |