Proof of Theorem elgiso
| Step | Hyp | Ref
| Expression |
| 1 | | oprex 3983 |
. . . . 5
 GrpHom   |
| 2 | 1 | rabex 2725 |
. . . 4
  GrpHom 
      |
| 3 | | rneq 3339 |
. . . . . . 7

  |
| 4 | | f1oeq2 3685 |
. . . . . . 7

            |
| 5 | 3, 4 | syl 10 |
. . . . . 6
             |
| 6 | 5 | rabbisdv 1807 |
. . . . 5
   GrpHom         GrpHom         |
| 7 | | opreq1 3968 |
. . . . . 6
  GrpHom   GrpHom    |
| 8 | | rabeq 1809 |
. . . . . 6
  GrpHom   GrpHom 
  GrpHom 
       GrpHom         |
| 9 | 7, 8 | syl 10 |
. . . . 5
   GrpHom         GrpHom         |
| 10 | 6, 9 | eqtrd 1507 |
. . . 4
   GrpHom         GrpHom         |
| 11 | | rneq 3339 |
. . . . . . 7

  |
| 12 | | f1oeq3 3686 |
. . . . . . 7

            |
| 13 | 11, 12 | syl 10 |
. . . . . 6
             |
| 14 | 13 | rabbisdv 1807 |
. . . . 5
   GrpHom         GrpHom         |
| 15 | | opreq2 3969 |
. . . . . 6
  GrpHom   GrpHom    |
| 16 | | rabeq 1809 |
. . . . . 6
  GrpHom   GrpHom 
  GrpHom 
       GrpHom         |
| 17 | 15, 16 | syl 10 |
. . . . 5
   GrpHom         GrpHom         |
| 18 | 14, 17 | eqtrd 1507 |
. . . 4
   GrpHom         GrpHom         |
| 19 | | df-giso 10381 |
. . . 4
GrpIso          Grp Grp   GrpHom          |
| 20 | 2, 10, 18, 19 | oprabval2 4028 |
. . 3
  Grp
Grp 
GrpIso    GrpHom         |
| 21 | 20 | eleq2d 1541 |
. 2
  Grp
Grp   GrpIso    GrpHom          |
| 22 | | f1oeq1 3684 |
. . 3
             |
| 23 | 22 | elrab 1905 |
. 2

  GrpHom 
       GrpHom         |
| 24 | 21, 23 | syl6bb 536 |
1
  Grp
Grp   GrpIso    GrpHom   
      |