| Step | Hyp | Ref | Expression | 
						
							| 1 |  | breq1 | ⊢ ( 𝑥  =  𝑦  →  ( 𝑥  ≼  𝐵  ↔  𝑦  ≼  𝐵 ) ) | 
						
							| 2 |  | eleq1 | ⊢ ( 𝑥  =  𝑦  →  ( 𝑥  ∈  𝑈  ↔  𝑦  ∈  𝑈 ) ) | 
						
							| 3 | 1 2 | imbi12d | ⊢ ( 𝑥  =  𝑦  →  ( ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 )  ↔  ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) ) ) | 
						
							| 4 | 3 | imbi2d | ⊢ ( 𝑥  =  𝑦  →  ( ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) )  ↔  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) ) ) ) | 
						
							| 5 |  | breq1 | ⊢ ( 𝑥  =  𝐴  →  ( 𝑥  ≼  𝐵  ↔  𝐴  ≼  𝐵 ) ) | 
						
							| 6 |  | eleq1 | ⊢ ( 𝑥  =  𝐴  →  ( 𝑥  ∈  𝑈  ↔  𝐴  ∈  𝑈 ) ) | 
						
							| 7 | 5 6 | imbi12d | ⊢ ( 𝑥  =  𝐴  →  ( ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 )  ↔  ( 𝐴  ≼  𝐵  →  𝐴  ∈  𝑈 ) ) ) | 
						
							| 8 | 7 | imbi2d | ⊢ ( 𝑥  =  𝐴  →  ( ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) )  ↔  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝐴  ≼  𝐵  →  𝐴  ∈  𝑈 ) ) ) ) | 
						
							| 9 |  | r19.21v | ⊢ ( ∀ 𝑦  ∈  𝑥 ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) )  ↔  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) ) ) | 
						
							| 10 |  | simpl1 | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  𝑥  ∈  On ) | 
						
							| 11 |  | vex | ⊢ 𝑥  ∈  V | 
						
							| 12 |  | onelss | ⊢ ( 𝑥  ∈  On  →  ( 𝑦  ∈  𝑥  →  𝑦  ⊆  𝑥 ) ) | 
						
							| 13 | 12 | imp | ⊢ ( ( 𝑥  ∈  On  ∧  𝑦  ∈  𝑥 )  →  𝑦  ⊆  𝑥 ) | 
						
							| 14 |  | ssdomg | ⊢ ( 𝑥  ∈  V  →  ( 𝑦  ⊆  𝑥  →  𝑦  ≼  𝑥 ) ) | 
						
							| 15 | 11 13 14 | mpsyl | ⊢ ( ( 𝑥  ∈  On  ∧  𝑦  ∈  𝑥 )  →  𝑦  ≼  𝑥 ) | 
						
							| 16 | 10 15 | sylan | ⊢ ( ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  ∧  𝑦  ∈  𝑥 )  →  𝑦  ≼  𝑥 ) | 
						
							| 17 |  | simplr | ⊢ ( ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  ∧  𝑦  ∈  𝑥 )  →  𝑥  ≼  𝐵 ) | 
						
							| 18 |  | domtr | ⊢ ( ( 𝑦  ≼  𝑥  ∧  𝑥  ≼  𝐵 )  →  𝑦  ≼  𝐵 ) | 
						
							| 19 | 16 17 18 | syl2anc | ⊢ ( ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  ∧  𝑦  ∈  𝑥 )  →  𝑦  ≼  𝐵 ) | 
						
							| 20 |  | pm2.27 | ⊢ ( 𝑦  ≼  𝐵  →  ( ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  𝑦  ∈  𝑈 ) ) | 
						
							| 21 | 19 20 | syl | ⊢ ( ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  ∧  𝑦  ∈  𝑥 )  →  ( ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  𝑦  ∈  𝑈 ) ) | 
						
							| 22 | 21 | ralimdva | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  ∀ 𝑦  ∈  𝑥 𝑦  ∈  𝑈 ) ) | 
						
							| 23 |  | dfss3 | ⊢ ( 𝑥  ⊆  𝑈  ↔  ∀ 𝑦  ∈  𝑥 𝑦  ∈  𝑈 ) | 
						
							| 24 |  | domeng | ⊢ ( 𝐵  ∈  𝑈  →  ( 𝑥  ≼  𝐵  ↔  ∃ 𝑦 ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 ) ) ) | 
						
							| 25 | 24 | 3ad2ant3 | ⊢ ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  ↔  ∃ 𝑦 ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 ) ) ) | 
						
							| 26 | 25 | biimpa | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ∃ 𝑦 ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 ) ) | 
						
							| 27 |  | simpl2 | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  𝑈  ∈  Univ ) | 
						
							| 28 |  | gruss | ⊢ ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈  ∧  𝑦  ⊆  𝐵 )  →  𝑦  ∈  𝑈 ) | 
						
							| 29 | 28 | 3expia | ⊢ ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑦  ⊆  𝐵  →  𝑦  ∈  𝑈 ) ) | 
						
							| 30 | 29 | 3adant1 | ⊢ ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑦  ⊆  𝐵  →  𝑦  ∈  𝑈 ) ) | 
						
							| 31 | 30 | adantr | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( 𝑦  ⊆  𝐵  →  𝑦  ∈  𝑈 ) ) | 
						
							| 32 |  | ensym | ⊢ ( 𝑥  ≈  𝑦  →  𝑦  ≈  𝑥 ) | 
						
							| 33 | 31 32 | anim12d1 | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ( 𝑦  ⊆  𝐵  ∧  𝑥  ≈  𝑦 )  →  ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 ) ) ) | 
						
							| 34 | 33 | ancomsd | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 )  →  ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 ) ) ) | 
						
							| 35 | 34 | eximdv | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ∃ 𝑦 ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 )  →  ∃ 𝑦 ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 ) ) ) | 
						
							| 36 |  | gruen | ⊢ ( ( 𝑈  ∈  Univ  ∧  𝑥  ⊆  𝑈  ∧  ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 ) )  →  𝑥  ∈  𝑈 ) | 
						
							| 37 | 36 | 3com23 | ⊢ ( ( 𝑈  ∈  Univ  ∧  ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 )  ∧  𝑥  ⊆  𝑈 )  →  𝑥  ∈  𝑈 ) | 
						
							| 38 | 37 | 3exp | ⊢ ( 𝑈  ∈  Univ  →  ( ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 )  →  ( 𝑥  ⊆  𝑈  →  𝑥  ∈  𝑈 ) ) ) | 
						
							| 39 | 38 | exlimdv | ⊢ ( 𝑈  ∈  Univ  →  ( ∃ 𝑦 ( 𝑦  ∈  𝑈  ∧  𝑦  ≈  𝑥 )  →  ( 𝑥  ⊆  𝑈  →  𝑥  ∈  𝑈 ) ) ) | 
						
							| 40 | 27 35 39 | sylsyld | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ∃ 𝑦 ( 𝑥  ≈  𝑦  ∧  𝑦  ⊆  𝐵 )  →  ( 𝑥  ⊆  𝑈  →  𝑥  ∈  𝑈 ) ) ) | 
						
							| 41 | 26 40 | mpd | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( 𝑥  ⊆  𝑈  →  𝑥  ∈  𝑈 ) ) | 
						
							| 42 | 23 41 | biimtrrid | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ∀ 𝑦  ∈  𝑥 𝑦  ∈  𝑈  →  𝑥  ∈  𝑈 ) ) | 
						
							| 43 | 22 42 | syld | ⊢ ( ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  ∧  𝑥  ≼  𝐵 )  →  ( ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  𝑥  ∈  𝑈 ) ) | 
						
							| 44 | 43 | ex | ⊢ ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  ( ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  𝑥  ∈  𝑈 ) ) ) | 
						
							| 45 | 44 | com23 | ⊢ ( ( 𝑥  ∈  On  ∧  𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) ) ) | 
						
							| 46 | 45 | 3expib | ⊢ ( 𝑥  ∈  On  →  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) ) ) ) | 
						
							| 47 | 46 | a2d | ⊢ ( 𝑥  ∈  On  →  ( ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ∀ 𝑦  ∈  𝑥 ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) )  →  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) ) ) ) | 
						
							| 48 | 9 47 | biimtrid | ⊢ ( 𝑥  ∈  On  →  ( ∀ 𝑦  ∈  𝑥 ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑦  ≼  𝐵  →  𝑦  ∈  𝑈 ) )  →  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝑥  ≼  𝐵  →  𝑥  ∈  𝑈 ) ) ) ) | 
						
							| 49 | 4 8 48 | tfis3 | ⊢ ( 𝐴  ∈  On  →  ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝐴  ≼  𝐵  →  𝐴  ∈  𝑈 ) ) ) | 
						
							| 50 | 49 | com3l | ⊢ ( ( 𝑈  ∈  Univ  ∧  𝐵  ∈  𝑈 )  →  ( 𝐴  ≼  𝐵  →  ( 𝐴  ∈  On  →  𝐴  ∈  𝑈 ) ) ) | 
						
							| 51 | 50 | impr | ⊢ ( ( 𝑈  ∈  Univ  ∧  ( 𝐵  ∈  𝑈  ∧  𝐴  ≼  𝐵 ) )  →  ( 𝐴  ∈  On  →  𝐴  ∈  𝑈 ) ) | 
						
							| 52 | 51 | 3impia | ⊢ ( ( 𝑈  ∈  Univ  ∧  ( 𝐵  ∈  𝑈  ∧  𝐴  ≼  𝐵 )  ∧  𝐴  ∈  On )  →  𝐴  ∈  𝑈 ) | 
						
							| 53 | 52 | 3com23 | ⊢ ( ( 𝑈  ∈  Univ  ∧  𝐴  ∈  On  ∧  ( 𝐵  ∈  𝑈  ∧  𝐴  ≼  𝐵 ) )  →  𝐴  ∈  𝑈 ) |