| Step | Hyp | Ref | Expression | 
						
							| 1 |  | breq1 | ⊢ ( 𝑥  =  ∅  →  ( 𝑥  ≈  𝑧  ↔  ∅  ≈  𝑧 ) ) | 
						
							| 2 |  | eqeq1 | ⊢ ( 𝑥  =  ∅  →  ( 𝑥  =  𝑧  ↔  ∅  =  𝑧 ) ) | 
						
							| 3 | 1 2 | imbi12d | ⊢ ( 𝑥  =  ∅  →  ( ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ( ∅  ≈  𝑧  →  ∅  =  𝑧 ) ) ) | 
						
							| 4 | 3 | ralbidv | ⊢ ( 𝑥  =  ∅  →  ( ∀ 𝑧  ∈  ω ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ∀ 𝑧  ∈  ω ( ∅  ≈  𝑧  →  ∅  =  𝑧 ) ) ) | 
						
							| 5 |  | breq1 | ⊢ ( 𝑥  =  𝑦  →  ( 𝑥  ≈  𝑧  ↔  𝑦  ≈  𝑧 ) ) | 
						
							| 6 |  | eqeq1 | ⊢ ( 𝑥  =  𝑦  →  ( 𝑥  =  𝑧  ↔  𝑦  =  𝑧 ) ) | 
						
							| 7 | 5 6 | imbi12d | ⊢ ( 𝑥  =  𝑦  →  ( ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) ) ) | 
						
							| 8 | 7 | ralbidv | ⊢ ( 𝑥  =  𝑦  →  ( ∀ 𝑧  ∈  ω ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) ) ) | 
						
							| 9 |  | breq1 | ⊢ ( 𝑥  =  suc  𝑦  →  ( 𝑥  ≈  𝑧  ↔  suc  𝑦  ≈  𝑧 ) ) | 
						
							| 10 |  | eqeq1 | ⊢ ( 𝑥  =  suc  𝑦  →  ( 𝑥  =  𝑧  ↔  suc  𝑦  =  𝑧 ) ) | 
						
							| 11 | 9 10 | imbi12d | ⊢ ( 𝑥  =  suc  𝑦  →  ( ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ( suc  𝑦  ≈  𝑧  →  suc  𝑦  =  𝑧 ) ) ) | 
						
							| 12 | 11 | ralbidv | ⊢ ( 𝑥  =  suc  𝑦  →  ( ∀ 𝑧  ∈  ω ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ∀ 𝑧  ∈  ω ( suc  𝑦  ≈  𝑧  →  suc  𝑦  =  𝑧 ) ) ) | 
						
							| 13 |  | breq1 | ⊢ ( 𝑥  =  𝐴  →  ( 𝑥  ≈  𝑧  ↔  𝐴  ≈  𝑧 ) ) | 
						
							| 14 |  | eqeq1 | ⊢ ( 𝑥  =  𝐴  →  ( 𝑥  =  𝑧  ↔  𝐴  =  𝑧 ) ) | 
						
							| 15 | 13 14 | imbi12d | ⊢ ( 𝑥  =  𝐴  →  ( ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ( 𝐴  ≈  𝑧  →  𝐴  =  𝑧 ) ) ) | 
						
							| 16 | 15 | ralbidv | ⊢ ( 𝑥  =  𝐴  →  ( ∀ 𝑧  ∈  ω ( 𝑥  ≈  𝑧  →  𝑥  =  𝑧 )  ↔  ∀ 𝑧  ∈  ω ( 𝐴  ≈  𝑧  →  𝐴  =  𝑧 ) ) ) | 
						
							| 17 |  | ensym | ⊢ ( ∅  ≈  𝑧  →  𝑧  ≈  ∅ ) | 
						
							| 18 |  | en0 | ⊢ ( 𝑧  ≈  ∅  ↔  𝑧  =  ∅ ) | 
						
							| 19 |  | eqcom | ⊢ ( 𝑧  =  ∅  ↔  ∅  =  𝑧 ) | 
						
							| 20 | 18 19 | bitri | ⊢ ( 𝑧  ≈  ∅  ↔  ∅  =  𝑧 ) | 
						
							| 21 | 17 20 | sylib | ⊢ ( ∅  ≈  𝑧  →  ∅  =  𝑧 ) | 
						
							| 22 | 21 | rgenw | ⊢ ∀ 𝑧  ∈  ω ( ∅  ≈  𝑧  →  ∅  =  𝑧 ) | 
						
							| 23 |  | nn0suc | ⊢ ( 𝑤  ∈  ω  →  ( 𝑤  =  ∅  ∨  ∃ 𝑧  ∈  ω 𝑤  =  suc  𝑧 ) ) | 
						
							| 24 |  | en0 | ⊢ ( suc  𝑦  ≈  ∅  ↔  suc  𝑦  =  ∅ ) | 
						
							| 25 |  | breq2 | ⊢ ( 𝑤  =  ∅  →  ( suc  𝑦  ≈  𝑤  ↔  suc  𝑦  ≈  ∅ ) ) | 
						
							| 26 |  | eqeq2 | ⊢ ( 𝑤  =  ∅  →  ( suc  𝑦  =  𝑤  ↔  suc  𝑦  =  ∅ ) ) | 
						
							| 27 | 25 26 | bibi12d | ⊢ ( 𝑤  =  ∅  →  ( ( suc  𝑦  ≈  𝑤  ↔  suc  𝑦  =  𝑤 )  ↔  ( suc  𝑦  ≈  ∅  ↔  suc  𝑦  =  ∅ ) ) ) | 
						
							| 28 | 24 27 | mpbiri | ⊢ ( 𝑤  =  ∅  →  ( suc  𝑦  ≈  𝑤  ↔  suc  𝑦  =  𝑤 ) ) | 
						
							| 29 | 28 | biimpd | ⊢ ( 𝑤  =  ∅  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) | 
						
							| 30 | 29 | a1i | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( 𝑤  =  ∅  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) | 
						
							| 31 |  | nfv | ⊢ Ⅎ 𝑧 𝑦  ∈  ω | 
						
							| 32 |  | nfra1 | ⊢ Ⅎ 𝑧 ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) | 
						
							| 33 | 31 32 | nfan | ⊢ Ⅎ 𝑧 ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) ) | 
						
							| 34 |  | nfv | ⊢ Ⅎ 𝑧 ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) | 
						
							| 35 |  | vex | ⊢ 𝑦  ∈  V | 
						
							| 36 |  | vex | ⊢ 𝑧  ∈  V | 
						
							| 37 | 35 36 | phplem4OLD | ⊢ ( ( 𝑦  ∈  ω  ∧  𝑧  ∈  ω )  →  ( suc  𝑦  ≈  suc  𝑧  →  𝑦  ≈  𝑧 ) ) | 
						
							| 38 | 37 | imim1d | ⊢ ( ( 𝑦  ∈  ω  ∧  𝑧  ∈  ω )  →  ( ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ( suc  𝑦  ≈  suc  𝑧  →  𝑦  =  𝑧 ) ) ) | 
						
							| 39 | 38 | ex | ⊢ ( 𝑦  ∈  ω  →  ( 𝑧  ∈  ω  →  ( ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ( suc  𝑦  ≈  suc  𝑧  →  𝑦  =  𝑧 ) ) ) ) | 
						
							| 40 | 39 | a2d | ⊢ ( 𝑦  ∈  ω  →  ( ( 𝑧  ∈  ω  →  ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( 𝑧  ∈  ω  →  ( suc  𝑦  ≈  suc  𝑧  →  𝑦  =  𝑧 ) ) ) ) | 
						
							| 41 |  | rsp | ⊢ ( ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ( 𝑧  ∈  ω  →  ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) ) ) | 
						
							| 42 | 40 41 | impel | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( 𝑧  ∈  ω  →  ( suc  𝑦  ≈  suc  𝑧  →  𝑦  =  𝑧 ) ) ) | 
						
							| 43 |  | suceq | ⊢ ( 𝑦  =  𝑧  →  suc  𝑦  =  suc  𝑧 ) | 
						
							| 44 | 42 43 | syl8 | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( 𝑧  ∈  ω  →  ( suc  𝑦  ≈  suc  𝑧  →  suc  𝑦  =  suc  𝑧 ) ) ) | 
						
							| 45 |  | breq2 | ⊢ ( 𝑤  =  suc  𝑧  →  ( suc  𝑦  ≈  𝑤  ↔  suc  𝑦  ≈  suc  𝑧 ) ) | 
						
							| 46 |  | eqeq2 | ⊢ ( 𝑤  =  suc  𝑧  →  ( suc  𝑦  =  𝑤  ↔  suc  𝑦  =  suc  𝑧 ) ) | 
						
							| 47 | 45 46 | imbi12d | ⊢ ( 𝑤  =  suc  𝑧  →  ( ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 )  ↔  ( suc  𝑦  ≈  suc  𝑧  →  suc  𝑦  =  suc  𝑧 ) ) ) | 
						
							| 48 | 47 | biimprcd | ⊢ ( ( suc  𝑦  ≈  suc  𝑧  →  suc  𝑦  =  suc  𝑧 )  →  ( 𝑤  =  suc  𝑧  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) | 
						
							| 49 | 44 48 | syl6 | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( 𝑧  ∈  ω  →  ( 𝑤  =  suc  𝑧  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) ) | 
						
							| 50 | 33 34 49 | rexlimd | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( ∃ 𝑧  ∈  ω 𝑤  =  suc  𝑧  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) | 
						
							| 51 | 30 50 | jaod | ⊢ ( ( 𝑦  ∈  ω  ∧  ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 ) )  →  ( ( 𝑤  =  ∅  ∨  ∃ 𝑧  ∈  ω 𝑤  =  suc  𝑧 )  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) | 
						
							| 52 | 51 | ex | ⊢ ( 𝑦  ∈  ω  →  ( ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ( ( 𝑤  =  ∅  ∨  ∃ 𝑧  ∈  ω 𝑤  =  suc  𝑧 )  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) ) | 
						
							| 53 | 23 52 | syl7 | ⊢ ( 𝑦  ∈  ω  →  ( ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ( 𝑤  ∈  ω  →  ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) ) | 
						
							| 54 | 53 | ralrimdv | ⊢ ( 𝑦  ∈  ω  →  ( ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ∀ 𝑤  ∈  ω ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 ) ) ) | 
						
							| 55 |  | breq2 | ⊢ ( 𝑤  =  𝑧  →  ( suc  𝑦  ≈  𝑤  ↔  suc  𝑦  ≈  𝑧 ) ) | 
						
							| 56 |  | eqeq2 | ⊢ ( 𝑤  =  𝑧  →  ( suc  𝑦  =  𝑤  ↔  suc  𝑦  =  𝑧 ) ) | 
						
							| 57 | 55 56 | imbi12d | ⊢ ( 𝑤  =  𝑧  →  ( ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 )  ↔  ( suc  𝑦  ≈  𝑧  →  suc  𝑦  =  𝑧 ) ) ) | 
						
							| 58 | 57 | cbvralvw | ⊢ ( ∀ 𝑤  ∈  ω ( suc  𝑦  ≈  𝑤  →  suc  𝑦  =  𝑤 )  ↔  ∀ 𝑧  ∈  ω ( suc  𝑦  ≈  𝑧  →  suc  𝑦  =  𝑧 ) ) | 
						
							| 59 | 54 58 | imbitrdi | ⊢ ( 𝑦  ∈  ω  →  ( ∀ 𝑧  ∈  ω ( 𝑦  ≈  𝑧  →  𝑦  =  𝑧 )  →  ∀ 𝑧  ∈  ω ( suc  𝑦  ≈  𝑧  →  suc  𝑦  =  𝑧 ) ) ) | 
						
							| 60 | 4 8 12 16 22 59 | finds | ⊢ ( 𝐴  ∈  ω  →  ∀ 𝑧  ∈  ω ( 𝐴  ≈  𝑧  →  𝐴  =  𝑧 ) ) | 
						
							| 61 |  | breq2 | ⊢ ( 𝑧  =  𝐵  →  ( 𝐴  ≈  𝑧  ↔  𝐴  ≈  𝐵 ) ) | 
						
							| 62 |  | eqeq2 | ⊢ ( 𝑧  =  𝐵  →  ( 𝐴  =  𝑧  ↔  𝐴  =  𝐵 ) ) | 
						
							| 63 | 61 62 | imbi12d | ⊢ ( 𝑧  =  𝐵  →  ( ( 𝐴  ≈  𝑧  →  𝐴  =  𝑧 )  ↔  ( 𝐴  ≈  𝐵  →  𝐴  =  𝐵 ) ) ) | 
						
							| 64 | 63 | rspcv | ⊢ ( 𝐵  ∈  ω  →  ( ∀ 𝑧  ∈  ω ( 𝐴  ≈  𝑧  →  𝐴  =  𝑧 )  →  ( 𝐴  ≈  𝐵  →  𝐴  =  𝐵 ) ) ) | 
						
							| 65 | 60 64 | mpan9 | ⊢ ( ( 𝐴  ∈  ω  ∧  𝐵  ∈  ω )  →  ( 𝐴  ≈  𝐵  →  𝐴  =  𝐵 ) ) | 
						
							| 66 |  | eqeng | ⊢ ( 𝐴  ∈  ω  →  ( 𝐴  =  𝐵  →  𝐴  ≈  𝐵 ) ) | 
						
							| 67 | 66 | adantr | ⊢ ( ( 𝐴  ∈  ω  ∧  𝐵  ∈  ω )  →  ( 𝐴  =  𝐵  →  𝐴  ≈  𝐵 ) ) | 
						
							| 68 | 65 67 | impbid | ⊢ ( ( 𝐴  ∈  ω  ∧  𝐵  ∈  ω )  →  ( 𝐴  ≈  𝐵  ↔  𝐴  =  𝐵 ) ) |