| Step | Hyp | Ref
 | Expression | 
| 1 |   | vex 2863 | 
. . . . . . 7
        | 
| 2 | 1 | elimak 4260 | 
. . . . . 6
          Sk     1    k     k1c         1c       
    Sk     1    k      | 
| 3 |   | el1c 4140 | 
. . . . . . . . . 10
       1c     
         | 
| 4 | 3 | anbi1i 676 | 
. . . . . . . . 9
       
1c              Sk     1    k             
              
    Sk     1    k       | 
| 5 |   | 19.41v 1901 | 
. . . . . . . . 9
                      
    Sk     1    k             
              
    Sk     1    k       | 
| 6 | 4, 5 | bitr4i 243 | 
. . . . . . . 8
       
1c              Sk     1    k            
              
    Sk     1    k       | 
| 7 | 6 | exbii 1582 | 
. . . . . . 7
          1c              Sk     1    k                                  Sk     1    k       | 
| 8 |   | df-rex 2621 | 
. . . . . . 7
       
1c            Sk     1    k           
  1c
        
    Sk     1    k       | 
| 9 |   | excom 1741 | 
. . . . . . 7
                             Sk     1    k                                  Sk     1    k       | 
| 10 | 7, 8, 9 | 3bitr4i 268 | 
. . . . . 6
       
1c            Sk     1    k                                 Sk     1    k       | 
| 11 | 2, 10 | bitri 240 | 
. . . . 5
          Sk     1    k     k1c          
              
    Sk     1    k       | 
| 12 |   | snex 4112 | 
. . . . . . . 8
       
  | 
| 13 |   | opkeq1 4060 | 
. . . . . . . . 9
                                | 
| 14 | 13 | eleq1d 2419 | 
. . . . . . . 8
                         Sk     1    k            
       Sk     1    k       | 
| 15 | 12, 14 | ceqsexv 2895 | 
. . . . . . 7
                      
    Sk     1    k             
       Sk     1    k      | 
| 16 |   | eldif 3222 | 
. . . . . . . 8
                Sk     1    k                   Sk                  1    k      | 
| 17 |   | vex 2863 | 
. . . . . . . . . 10
        | 
| 18 | 17, 1 | elssetk 4271 | 
. . . . . . . . 9
              Sk          | 
| 19 | 12, 1 | opkelxpk 4249 | 
. . . . . . . . . . . 12
                1    k              1             | 
| 20 | 1, 19 | mpbiran2 885 | 
. . . . . . . . . . 11
                1    k             1    | 
| 21 |   | snelpw1 4147 | 
. . . . . . . . . . 11
          1            | 
| 22 | 20, 21 | bitri 240 | 
. . . . . . . . . 10
                1    k             | 
| 23 | 22 | notbii 287 | 
. . . . . . . . 9
                  1    k   
 
         | 
| 24 | 18, 23 | anbi12i 678 | 
. . . . . . . 8
               Sk             
    1    k                     
    | 
| 25 |   | annim 414 | 
. . . . . . . 8
               
                          | 
| 26 | 16, 24, 25 | 3bitri 262 | 
. . . . . . 7
                Sk     1    k             
       
    | 
| 27 | 15, 26 | bitri 240 | 
. . . . . 6
                      
    Sk     1    k              
       
    | 
| 28 | 27 | exbii 1582 | 
. . . . 5
                             Sk     1    k                              | 
| 29 |   | exnal 1574 | 
. . . . 5
                                               | 
| 30 | 11, 28, 29 | 3bitri 262 | 
. . . 4
          Sk     1    k     k1c                    
    | 
| 31 | 30 | con2bii 322 | 
. . 3
                                Sk     1    k     k1c   | 
| 32 | 1 | elpw 3729 | 
. . . 4
                   | 
| 33 |   | dfss2 3263 | 
. . . 4
                         
    | 
| 34 | 32, 33 | bitri 240 | 
. . 3
                
              | 
| 35 | 1 | elcompl 3226 | 
. . 3
       ∼    Sk     1    k     k1c             Sk     1    k     k1c   | 
| 36 | 31, 34, 35 | 3bitr4i 268 | 
. 2
                ∼   
Sk     1    k     k1c   | 
| 37 | 36 | eqriv 2350 | 
1
       ∼    Sk     1    k     k1c  |