| Step | Hyp | Ref
| Expression |
| 1 | | df-meas 30259 |
. . . 4
measures   sigAlgebra                 
Disj       Σ*           |
| 2 | | vex 3203 |
. . . . . 6
 |
| 3 | | ovex 6678 |
. . . . . 6
    |
| 4 | | mapex 7863 |
. . . . . 6
    
            |
| 5 | 2, 3, 4 | mp2an 708 |
. . . . 5
        
 |
| 6 | | simp1 1061 |
. . . . . 6
                
Disj       Σ*                 |
| 7 | 6 | ss2abi 3674 |
. . . . 5
        
       
Disj       Σ*        
          |
| 8 | 5, 7 | ssexi 4803 |
. . . 4
        
       
Disj       Σ*          |
| 9 | | feq1 6026 |
. . . . 5
                   |
| 10 | | fveq1 6190 |
. . . . . 6
           |
| 11 | 10 | eqeq1d 2624 |
. . . . 5
             |
| 12 | | fveq1 6190 |
. . . . . . . 8
             |
| 13 | | fveq1 6190 |
. . . . . . . . 9
           |
| 14 | 13 | esumeq2sdv 30101 |
. . . . . . . 8

Σ*     
Σ*        |
| 15 | 12, 14 | eqeq12d 2637 |
. . . . . . 7
       Σ*     
     Σ*         |
| 16 | 15 | imbi2d 330 |
. . . . . 6
    Disj 
     Σ*         Disj 
     Σ*          |
| 17 | 16 | ralbidv 2986 |
. . . . 5
  
  
Disj       Σ*          
Disj       Σ*          |
| 18 | 9, 11, 17 | 3anbi123d 1399 |
. . . 4
                 
Disj       Σ*       
               
Disj       Σ*           |
| 19 | 1, 8, 18 | abfmpunirn 29452 |
. . 3
  measures
  
sigAlgebra       
       
Disj       Σ*           |
| 20 | 19 | simprbi 480 |
. 2
  measures  
sigAlgebra       
       
Disj       Σ*          |
| 21 | | fdm 6051 |
. . . . . . 7
          |
| 22 | 21 | 3ad2ant1 1082 |
. . . . . 6
                
Disj       Σ*       
  |
| 23 | 22 | adantl 482 |
. . . . 5
   sigAlgebra                
Disj       Σ*        
  |
| 24 | | simpl 473 |
. . . . 5
   sigAlgebra                
Disj       Σ*        
 sigAlgebra |
| 25 | 23, 24 | eqeltrd 2701 |
. . . 4
   sigAlgebra                
Disj       Σ*        

sigAlgebra |
| 26 | | simp1 1061 |
. . . . . . 7
                
Disj       Σ*                 |
| 27 | | feq2 6027 |
. . . . . . . 8
                   |
| 28 | 27 | biimpar 502 |
. . . . . . 7
                   |
| 29 | 22, 26, 28 | syl2anc 693 |
. . . . . 6
                
Disj       Σ*                 |
| 30 | | simp2 1062 |
. . . . . 6
                
Disj       Σ*              |
| 31 | | simp3 1063 |
. . . . . . 7
                
Disj       Σ*           
Disj       Σ*         |
| 32 | | pweq 4161 |
. . . . . . . . 9
     |
| 33 | 32 | raleqdv 3144 |
. . . . . . . 8
  
   Disj       Σ*      
   
Disj       Σ*          |
| 34 | 33 | biimpar 502 |
. . . . . . 7
     
Disj       Σ*           
Disj       Σ*         |
| 35 | 22, 31, 34 | syl2anc 693 |
. . . . . 6
                
Disj       Σ*           
Disj       Σ*         |
| 36 | 29, 30, 35 | 3jca 1242 |
. . . . 5
                
Disj       Σ*               
        Disj       Σ*          |
| 37 | 36 | adantl 482 |
. . . 4
   sigAlgebra                
Disj       Σ*        
                Disj       Σ*          |
| 38 | 25, 37 | jca 554 |
. . 3
   sigAlgebra                
Disj       Σ*        
  sigAlgebra                 Disj       Σ*           |
| 39 | 38 | rexlimiva 3028 |
. 2
   sigAlgebra               
Disj       Σ*         
sigAlgebra                 Disj       Σ*           |
| 40 | 20, 39 | syl 17 |
1
  measures   sigAlgebra                
Disj       Σ*           |