| Step | Hyp | Ref
| Expression |
| 1 | | wrdfn 13319 |
. . . . . . 7
 Word  ..^       |
| 2 | 1 | ad2antrr 762 |
. . . . . 6
   Word       ..^     
 ..^       |
| 3 | | lencl 13324 |
. . . . . . . . . . . . 13
 Word       |
| 4 | 3 | nn0zd 11480 |
. . . . . . . . . . . 12
 Word       |
| 5 | | fzoval 12471 |
. . . . . . . . . . . 12
    
 ..^                 |
| 6 | 4, 5 | syl 17 |
. . . . . . . . . . 11
 Word  ..^                 |
| 7 | 6 | adantr 481 |
. . . . . . . . . 10
  Word       ..^                 |
| 8 | 7 | eleq2d 2687 |
. . . . . . . . 9
  Word        ..^    
             |
| 9 | 8 | biimpa 501 |
. . . . . . . 8
   Word       ..^     
            |
| 10 | | fznn0sub2 12446 |
. . . . . . . 8
          
                    |
| 11 | 9, 10 | syl 17 |
. . . . . . 7
   Word       ..^                          |
| 12 | 7 | adantr 481 |
. . . . . . 7
   Word       ..^       ..^                 |
| 13 | 11, 12 | eleqtrrd 2704 |
. . . . . 6
   Word       ..^               ..^       |
| 14 | | fvco2 6273 |
. . . . . 6
   ..^              ..^                                      |
| 15 | 2, 13, 14 | syl2anc 693 |
. . . . 5
   Word       ..^                                      |
| 16 | | lenco 13578 |
. . . . . . . . 9
  Word         
        |
| 17 | 16 | oveq1d 6665 |
. . . . . . . 8
  Word                      |
| 18 | 17 | oveq1d 6665 |
. . . . . . 7
  Word                          |
| 19 | 18 | adantr 481 |
. . . . . 6
   Word       ..^                          |
| 20 | 19 | fveq2d 6195 |
. . . . 5
   Word       ..^                
                     |
| 21 | | revfv 13512 |
. . . . . . 7
  Word
 ..^       reverse                   |
| 22 | 21 | adantlr 751 |
. . . . . 6
   Word       ..^       reverse                   |
| 23 | 22 | fveq2d 6195 |
. . . . 5
   Word       ..^          reverse                        |
| 24 | 15, 20, 23 | 3eqtr4d 2666 |
. . . 4
   Word       ..^                
         reverse        |
| 25 | 24 | mpteq2dva 4744 |
. . 3
  Word        ..^                        ..^         reverse         |
| 26 | 16 | oveq2d 6666 |
. . . 4
  Word       ..^        ..^       |
| 27 | 26 | mpteq1d 4738 |
. . 3
  Word        ..^                          ..^                        |
| 28 | | revlen 13511 |
. . . . . 6
 Word    reverse         |
| 29 | 28 | adantr 481 |
. . . . 5
  Word         reverse         |
| 30 | 29 | oveq2d 6666 |
. . . 4
  Word       ..^   reverse     ..^       |
| 31 | 30 | mpteq1d 4738 |
. . 3
  Word        ..^   reverse        reverse         ..^         reverse         |
| 32 | 25, 27, 31 | 3eqtr4rd 2667 |
. 2
  Word        ..^   reverse        reverse         ..^   
                      |
| 33 | | simpr 477 |
. . 3
  Word            |
| 34 | | revcl 13510 |
. . . . 5
 Word reverse  Word   |
| 35 | | wrdf 13310 |
. . . . 5
 reverse  Word reverse     ..^   reverse        |
| 36 | 34, 35 | syl 17 |
. . . 4
 Word reverse     ..^   reverse        |
| 37 | 36 | adantr 481 |
. . 3
  Word      reverse     ..^   reverse        |
| 38 | | fcompt 6400 |
. . 3
      reverse     ..^   reverse        reverse     ..^   reverse        reverse         |
| 39 | 33, 37, 38 | syl2anc 693 |
. 2
  Word       reverse     ..^   reverse        reverse         |
| 40 | | ffun 6048 |
. . . . 5
       |
| 41 | 40 | adantl 482 |
. . . 4
  Word     
  |
| 42 | | simpl 473 |
. . . 4
  Word      Word   |
| 43 | | cofunexg 7130 |
. . . 4
  Word  
   |
| 44 | 41, 42, 43 | syl2anc 693 |
. . 3
  Word          |
| 45 | | revval 13509 |
. . 3
   reverse      ..^   
                      |
| 46 | 44, 45 | syl 17 |
. 2
  Word      reverse      ..^   
                      |
| 47 | 32, 39, 46 | 3eqtr4d 2666 |
1
  Word       reverse   reverse 
    |