| Step | Hyp | Ref | Expression | 
						
							| 1 |  | sssucid | ⊢ 𝐴  ⊆  suc  𝐴 | 
						
							| 2 |  | trel | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  𝐴 )  →  𝑧  ∈  𝐴 ) ) | 
						
							| 3 | 2 | expd | ⊢ ( Tr  𝐴  →  ( 𝑧  ∈  𝑦  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 4 | 3 | adantrd | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 5 |  | ssel | ⊢ ( 𝐴  ⊆  suc  𝐴  →  ( 𝑧  ∈  𝐴  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 6 | 1 4 5 | ee03 | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  ( 𝑦  ∈  𝐴  →  𝑧  ∈  suc  𝐴 ) ) ) | 
						
							| 7 |  | simpl | ⊢ ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  𝑦 ) | 
						
							| 8 | 7 | a1i | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  𝑦 ) ) | 
						
							| 9 |  | eleq2 | ⊢ ( 𝑦  =  𝐴  →  ( 𝑧  ∈  𝑦  ↔  𝑧  ∈  𝐴 ) ) | 
						
							| 10 | 9 | biimpcd | ⊢ ( 𝑧  ∈  𝑦  →  ( 𝑦  =  𝐴  →  𝑧  ∈  𝐴 ) ) | 
						
							| 11 | 8 10 | syl6 | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  ( 𝑦  =  𝐴  →  𝑧  ∈  𝐴 ) ) ) | 
						
							| 12 | 1 11 5 | ee03 | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  ( 𝑦  =  𝐴  →  𝑧  ∈  suc  𝐴 ) ) ) | 
						
							| 13 |  | simpr | ⊢ ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑦  ∈  suc  𝐴 ) | 
						
							| 14 | 13 | a1i | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑦  ∈  suc  𝐴 ) ) | 
						
							| 15 |  | elsuci | ⊢ ( 𝑦  ∈  suc  𝐴  →  ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 ) ) | 
						
							| 16 | 14 15 | syl6 | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 ) ) ) | 
						
							| 17 |  | jao | ⊢ ( ( 𝑦  ∈  𝐴  →  𝑧  ∈  suc  𝐴 )  →  ( ( 𝑦  =  𝐴  →  𝑧  ∈  suc  𝐴 )  →  ( ( 𝑦  ∈  𝐴  ∨  𝑦  =  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) ) | 
						
							| 18 | 6 12 16 17 | ee222 | ⊢ ( Tr  𝐴  →  ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 19 | 18 | alrimivv | ⊢ ( Tr  𝐴  →  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 20 |  | dftr2 | ⊢ ( Tr  suc  𝐴  ↔  ∀ 𝑧 ∀ 𝑦 ( ( 𝑧  ∈  𝑦  ∧  𝑦  ∈  suc  𝐴 )  →  𝑧  ∈  suc  𝐴 ) ) | 
						
							| 21 | 19 20 | sylibr | ⊢ ( Tr  𝐴  →  Tr  suc  𝐴 ) |