| Step | Hyp | Ref | Expression | 
						
							| 1 |  | eluzel2 | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  𝑀  ∈  ℤ ) | 
						
							| 2 |  | fveq2 | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( ℤ≥ ‘ 𝑀 )  =  ( ℤ≥ ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ) ) | 
						
							| 3 | 2 | eleq2d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  ↔  𝑁  ∈  ( ℤ≥ ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ) ) ) | 
						
							| 4 |  | seqeq1 | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  seq 𝑀 (  +  ,  𝐹 )  =  seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ) | 
						
							| 5 | 4 | fveq1d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) ) ) | 
						
							| 6 | 4 | fveq1d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  =  ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ 𝑁 ) ) | 
						
							| 7 | 6 | oveq2d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) | 
						
							| 8 | 5 7 | eqeq12d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) )  ↔  ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) ) | 
						
							| 9 | 3 8 | imbi12d | ⊢ ( 𝑀  =  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  →  ( ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) ) )  ↔  ( 𝑁  ∈  ( ℤ≥ ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) )  →  ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) ) ) | 
						
							| 10 |  | 0z | ⊢ 0  ∈  ℤ | 
						
							| 11 | 10 | elimel | ⊢ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 )  ∈  ℤ | 
						
							| 12 |  | eqid | ⊢ ( rec ( ( 𝑥  ∈  V  ↦  ( 𝑥  +  1 ) ) ,  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) )  ↾  ω )  =  ( rec ( ( 𝑥  ∈  V  ↦  ( 𝑥  +  1 ) ) ,  if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) )  ↾  ω ) | 
						
							| 13 |  | fvex | ⊢ ( 𝐹 ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) )  ∈  V | 
						
							| 14 |  | eqid | ⊢ ( rec ( ( 𝑥  ∈  V ,  𝑦  ∈  V  ↦  〈 ( 𝑥  +  1 ) ,  ( 𝑥 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) 𝑦 ) 〉 ) ,  〈 if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ,  ( 𝐹 ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ) 〉 )  ↾  ω )  =  ( rec ( ( 𝑥  ∈  V ,  𝑦  ∈  V  ↦  〈 ( 𝑥  +  1 ) ,  ( 𝑥 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) 𝑦 ) 〉 ) ,  〈 if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ,  ( 𝐹 ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ) 〉 )  ↾  ω ) | 
						
							| 15 | 14 | seqval | ⊢ seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 )  =  ran  ( rec ( ( 𝑥  ∈  V ,  𝑦  ∈  V  ↦  〈 ( 𝑥  +  1 ) ,  ( 𝑥 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) 𝑦 ) 〉 ) ,  〈 if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ,  ( 𝐹 ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) ) 〉 )  ↾  ω ) | 
						
							| 16 | 11 12 13 14 15 | uzrdgsuci | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) )  →  ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq if ( 𝑀  ∈  ℤ ,  𝑀 ,  0 ) (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) | 
						
							| 17 | 9 16 | dedth | ⊢ ( 𝑀  ∈  ℤ  →  ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) ) | 
						
							| 18 | 1 17 | mpcom | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) ) ) | 
						
							| 19 |  | elex | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  𝑁  ∈  V ) | 
						
							| 20 |  | fvex | ⊢ ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  ∈  V | 
						
							| 21 |  | fvoveq1 | ⊢ ( 𝑧  =  𝑁  →  ( 𝐹 ‘ ( 𝑧  +  1 ) )  =  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) | 
						
							| 22 | 21 | oveq2d | ⊢ ( 𝑧  =  𝑁  →  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) )  =  ( 𝑤  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) ) | 
						
							| 23 |  | oveq1 | ⊢ ( 𝑤  =  ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  →  ( 𝑤  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) )  =  ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) ) | 
						
							| 24 |  | eqid | ⊢ ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) )  =  ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) | 
						
							| 25 |  | ovex | ⊢ ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) )  ∈  V | 
						
							| 26 | 22 23 24 25 | ovmpo | ⊢ ( ( 𝑁  ∈  V  ∧  ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  ∈  V )  →  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) )  =  ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) ) | 
						
							| 27 | 19 20 26 | sylancl | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  ( 𝑁 ( 𝑧  ∈  V ,  𝑤  ∈  V  ↦  ( 𝑤  +  ( 𝐹 ‘ ( 𝑧  +  1 ) ) ) ) ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 ) )  =  ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) ) | 
						
							| 28 | 18 27 | eqtrd | ⊢ ( 𝑁  ∈  ( ℤ≥ ‘ 𝑀 )  →  ( seq 𝑀 (  +  ,  𝐹 ) ‘ ( 𝑁  +  1 ) )  =  ( ( seq 𝑀 (  +  ,  𝐹 ) ‘ 𝑁 )  +  ( 𝐹 ‘ ( 𝑁  +  1 ) ) ) ) |