| Step | Hyp | Ref
| Expression |
| 1 | | s1eq 13380 |
. . . . 5
           |
| 2 | 1 | oveq2d 6666 |
. . . 4
  ++       ++        |
| 3 | 2 | eleq1d 2686 |
. . 3
   ++       ++         |
| 4 | 3 | reu8 3402 |
. 2
   ++         ++         ++     
    |
| 5 | | simprl 794 |
. . . . 5
    Word   Word                ++         ++     
    ++        |
| 6 | | simpl 473 |
. . . . . . . . . 10
  Word   Word            
Word   |
| 7 | 6 | ad2antrr 762 |
. . . . . . . . 9
    Word   Word                ++         ++     
   Word   |
| 8 | 7 | anim1i 592 |
. . . . . . . 8
     Word 
 Word
           
   ++     

  ++          
Word    |
| 9 | | simplrr 801 |
. . . . . . . 8
     Word 
 Word
           
   ++     

  ++          
  ++         |
| 10 | | simp-4r 807 |
. . . . . . . 8
     Word 
 Word
           
   ++     

  ++          
 Word              |
| 11 | | reuccatpfxs1lem 41433 |
. . . . . . . 8
   Word


  ++         Word            
  prefix       ++         |
| 12 | 8, 9, 10, 11 | syl3anc 1326 |
. . . . . . 7
     Word 
 Word
           
   ++     

  ++          
 prefix     
 ++
        |
| 13 | 6 | anim1i 592 |
. . . . . . . . . . . . . . . 16
   Word  
Word            
  Word
   |
| 14 | 13 | adantr 481 |
. . . . . . . . . . . . . . 15
    Word   Word                ++         ++     
    Word    |
| 15 | 14 | ad2antrr 762 |
. . . . . . . . . . . . . 14
      Word   Word            
   ++     

  ++           ++      
 Word    |
| 16 | | lswccats1 13411 |
. . . . . . . . . . . . . 14
  Word
 lastS   ++         |
| 17 | 15, 16 | syl 17 |
. . . . . . . . . . . . 13
      Word   Word            
   ++     

  ++           ++      
lastS   ++         |
| 18 | 17 | eqcomd 2628 |
. . . . . . . . . . . 12
      Word   Word            
   ++     

  ++           ++      
lastS   ++         |
| 19 | 18 | s1eqd 13381 |
. . . . . . . . . . 11
      Word   Word            
   ++     

  ++           ++      
      lastS   ++           |
| 20 | 19 | oveq2d 6666 |
. . . . . . . . . 10
      Word   Word            
   ++     

  ++           ++      
 ++     
 ++   lastS
  ++            |
| 21 | | id 22 |
. . . . . . . . . . . 12
  ++       ++        |
| 22 | | fveq2 6191 |
. . . . . . . . . . . . . 14
  ++      lastS  
lastS   ++         |
| 23 | 22 | s1eqd 13381 |
. . . . . . . . . . . . 13
  ++        lastS       lastS   ++           |
| 24 | 23 | oveq2d 6666 |
. . . . . . . . . . . 12
  ++       ++   lastS     
 ++   lastS
  ++            |
| 25 | 21, 24 | eqeq12d 2637 |
. . . . . . . . . . 11
  ++        ++   lastS       ++       ++   lastS   ++             |
| 26 | 25 | adantl 482 |
. . . . . . . . . 10
      Word   Word            
   ++     

  ++           ++      
  ++   lastS     
 ++     
 ++   lastS
  ++             |
| 27 | 20, 26 | mpbird 247 |
. . . . . . . . 9
      Word   Word            
   ++     

  ++           ++      
 ++
  lastS        |
| 28 | | eleq1 2689 |
. . . . . . . . . . . . . . . . . . 19
  Word
Word    |
| 29 | | fveq2 6191 |
. . . . . . . . . . . . . . . . . . . 20
           |
| 30 | 29 | eqeq1d 2624 |
. . . . . . . . . . . . . . . . . . 19
                         |
| 31 | 28, 30 | anbi12d 747 |
. . . . . . . . . . . . . . . . . 18
   Word             Word               |
| 32 | 31 | rspcva 3307 |
. . . . . . . . . . . . . . . . 17
    Word              Word              |
| 33 | | 3anass 1042 |
. . . . . . . . . . . . . . . . . 18
  Word
Word             Word  Word               |
| 34 | 33 | simplbi2com 657 |
. . . . . . . . . . . . . . . . 17
  Word            
Word 
Word Word               |
| 35 | 32, 34 | syl 17 |
. . . . . . . . . . . . . . . 16
    Word              Word  Word
Word               |
| 36 | 35 | ex 450 |
. . . . . . . . . . . . . . 15
  

Word            
Word 
Word Word                |
| 37 | 36 | com13 88 |
. . . . . . . . . . . . . 14
 Word  

Word              Word
Word                |
| 38 | 37 | imp 445 |
. . . . . . . . . . . . 13
  Word   Word               Word
Word               |
| 39 | 38 | ad2antrr 762 |
. . . . . . . . . . . 12
    Word   Word                ++         ++     
   
 Word Word               |
| 40 | 39 | imp 445 |
. . . . . . . . . . 11
     Word 
 Word
           
   ++     

  ++          
Word Word              |
| 41 | 40 | adantr 481 |
. . . . . . . . . 10
      Word   Word            
   ++     

  ++           ++      
 Word Word              |
| 42 | | ccats1pfxeqbi 41431 |
. . . . . . . . . 10
  Word
Word           
  prefix       ++   lastS         |
| 43 | 41, 42 | syl 17 |
. . . . . . . . 9
      Word   Word            
   ++     

  ++           ++      
  prefix       ++   lastS         |
| 44 | 27, 43 | mpbird 247 |
. . . . . . . 8
      Word   Word            
   ++     

  ++           ++      

prefix        |
| 45 | 44 | ex 450 |
. . . . . . 7
     Word 
 Word
           
   ++     

  ++            ++       prefix         |
| 46 | 12, 45 | impbid 202 |
. . . . . 6
     Word 
 Word
           
   ++     

  ++          
 prefix     
 ++         |
| 47 | 46 | ralrimiva 2966 |
. . . . 5
    Word   Word                ++         ++     
    
 prefix     
 ++
        |
| 48 | | reu6i 3397 |
. . . . 5
   ++       
 prefix     
 ++
         prefix        |
| 49 | 5, 47, 48 | syl2anc 693 |
. . . 4
    Word   Word                ++         ++     
     prefix        |
| 50 | 49 | ex 450 |
. . 3
   Word  
Word            
    ++     
   ++       


prefix         |
| 51 | 50 | rexlimdva 3031 |
. 2
  Word   Word                 ++     
   ++       


prefix         |
| 52 | 4, 51 | syl5bi 232 |
1
  Word   Word                ++     


prefix         |