| Step | Hyp | Ref | Expression | 
						
							| 1 |  | dftr2 | ⊢ ( Tr  suc  𝐴  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 2 |  | sssucid | ⊢ 𝐴  ⊆  suc  𝐴 | 
						
							| 3 |  | idn1 | ⊢ (    Tr  𝐴    ▶    Tr  𝐴    ) | 
						
							| 4 |  | idn2 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ) | 
						
							| 5 |  | simpl | ⊢ ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  𝑦 ) | 
						
							| 6 | 4 5 | e2 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    𝑧  ∈  𝑦    ) | 
						
							| 7 |  | idn3 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  ∈  𝐴    ▶    𝑦  ∈  𝐴    ) | 
						
							| 8 |  | trel | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) | 
						
							| 9 | 8 | expd | ⊢ ( Tr  𝐴  →  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 10 | 3 6 7 9 | e123 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  ∈  𝐴    ▶    𝑧  ∈  𝐴    ) | 
						
							| 11 |  | ssel | ⊢ ( 𝐴  ⊆  suc  𝐴  →  ( 𝑧  ∈  𝐴  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 12 | 2 10 11 | e03 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  ∈  𝐴    ▶    𝑧  ∈  suc  𝐴    ) | 
						
							| 13 | 12 | in3 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    ( 𝑦  ∈  𝐴  →  𝑧  ∈  suc  𝐴 )    ) | 
						
							| 14 |  | idn3 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  =  𝐴    ▶    𝑦  =  𝐴    ) | 
						
							| 15 |  | eleq2 | ⊢ ( 𝑦  =  𝐴  →  ( 𝑧  ∈  𝑦  ↔  𝑧  ∈  𝐴 ) ) | 
						
							| 16 | 15 | biimpcd | ⊢ ( 𝑧  ∈  𝑦  →  ( 𝑦  =  𝐴  →  𝑧  ∈  𝐴 ) ) | 
						
							| 17 | 6 14 16 | e23 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  =  𝐴    ▶    𝑧  ∈  𝐴    ) | 
						
							| 18 | 2 17 11 | e03 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ,    𝑦  =  𝐴    ▶    𝑧  ∈  suc  𝐴    ) | 
						
							| 19 | 18 | in3 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    ( 𝑦  =  𝐴  →  𝑧  ∈  suc  𝐴 )    ) | 
						
							| 20 |  | simpr | ⊢ ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑦  ∈  suc  𝐴 ) | 
						
							| 21 | 4 20 | e2 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    𝑦  ∈  suc  𝐴    ) | 
						
							| 22 |  | elsuci | ⊢ ( 𝑦  ∈  suc  𝐴  →  ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 ) ) | 
						
							| 23 | 21 22 | e2 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 )    ) | 
						
							| 24 |  | jao | ⊢ ( ( 𝑦  ∈  𝐴  →  𝑧  ∈  suc  𝐴 )  →  ( ( 𝑦  =  𝐴  →  𝑧  ∈  suc  𝐴 )  →  ( ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) ) | 
						
							| 25 | 13 19 23 24 | e222 | ⊢ (    Tr  𝐴    ,    ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )    ▶    𝑧  ∈  suc  𝐴    ) | 
						
							| 26 | 25 | in2 | ⊢ (    Tr  𝐴    ▶    ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 )    ) | 
						
							| 27 | 26 | gen12 | ⊢ (    Tr  𝐴    ▶    ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 )    ) | 
						
							| 28 |  | biimpr | ⊢ ( ( Tr  suc  𝐴  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 ) )  →  ( ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 )  →  Tr  suc  𝐴 ) ) | 
						
							| 29 | 1 27 28 | e01 | ⊢ (    Tr  𝐴    ▶    Tr  suc  𝐴    ) | 
						
							| 30 | 29 | in1 | ⊢ ( Tr  𝐴  →  Tr  suc  𝐴 ) |