| Step | Hyp | Ref | Expression | 
						
							| 1 |  | fvex | ⊢ ( 𝑓 ‘ 𝑎 )  ∈  V | 
						
							| 2 |  | fvex | ⊢ ( 𝑓 ‘ suc  𝑎 )  ∈  V | 
						
							| 3 | 2 | brresi | ⊢ ( ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 )  ↔  ( ( 𝑓 ‘ 𝑎 )  ∈  V  ∧  ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) ) | 
						
							| 4 | 1 3 | mpbiran | ⊢ ( ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 )  ↔  ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) | 
						
							| 5 | 4 | ralbii | ⊢ ( ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 )  ↔  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) | 
						
							| 6 | 5 | 3anbi3i | ⊢ ( ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 ) )  ↔  ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) ) | 
						
							| 7 | 6 | exbii | ⊢ ( ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 ) )  ↔  ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) ) | 
						
							| 8 | 7 | rexbii | ⊢ ( ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 ) )  ↔  ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) ) | 
						
							| 9 | 8 | opabbii | ⊢ { 〈 𝑥 ,  𝑦 〉  ∣  ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 ) ) }  =  { 〈 𝑥 ,  𝑦 〉  ∣  ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) } | 
						
							| 10 |  | df-ttrcl | ⊢ t++ ( 𝑅  ↾  V )  =  { 〈 𝑥 ,  𝑦 〉  ∣  ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) ( 𝑅  ↾  V ) ( 𝑓 ‘ suc  𝑎 ) ) } | 
						
							| 11 |  | df-ttrcl | ⊢ t++ 𝑅  =  { 〈 𝑥 ,  𝑦 〉  ∣  ∃ 𝑛  ∈  ( ω  ∖  1o ) ∃ 𝑓 ( 𝑓  Fn  suc  𝑛  ∧  ( ( 𝑓 ‘ ∅ )  =  𝑥  ∧  ( 𝑓 ‘ 𝑛 )  =  𝑦 )  ∧  ∀ 𝑎  ∈  𝑛 ( 𝑓 ‘ 𝑎 ) 𝑅 ( 𝑓 ‘ suc  𝑎 ) ) } | 
						
							| 12 | 9 10 11 | 3eqtr4i | ⊢ t++ ( 𝑅  ↾  V )  =  t++ 𝑅 |