| Step | Hyp | Ref | Expression | 
						
							| 1 |  | setsid.e | ⊢ 𝐸  =  Slot  ( 𝐸 ‘ ndx ) | 
						
							| 2 |  | setsnid.n | ⊢ ( 𝐸 ‘ ndx )  ≠  𝐷 | 
						
							| 3 |  | id | ⊢ ( 𝑊  ∈  V  →  𝑊  ∈  V ) | 
						
							| 4 | 1 3 | strfvnd | ⊢ ( 𝑊  ∈  V  →  ( 𝐸 ‘ 𝑊 )  =  ( 𝑊 ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 5 |  | ovex | ⊢ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  ∈  V | 
						
							| 6 | 5 1 | strfvn | ⊢ ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) )  =  ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ‘ ( 𝐸 ‘ ndx ) ) | 
						
							| 7 |  | setsres | ⊢ ( 𝑊  ∈  V  →  ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  ↾  ( V  ∖  { 𝐷 } ) )  =  ( 𝑊  ↾  ( V  ∖  { 𝐷 } ) ) ) | 
						
							| 8 | 7 | fveq1d | ⊢ ( 𝑊  ∈  V  →  ( ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) )  =  ( ( 𝑊  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 9 |  | fvex | ⊢ ( 𝐸 ‘ ndx )  ∈  V | 
						
							| 10 |  | eldifsn | ⊢ ( ( 𝐸 ‘ ndx )  ∈  ( V  ∖  { 𝐷 } )  ↔  ( ( 𝐸 ‘ ndx )  ∈  V  ∧  ( 𝐸 ‘ ndx )  ≠  𝐷 ) ) | 
						
							| 11 | 9 2 10 | mpbir2an | ⊢ ( 𝐸 ‘ ndx )  ∈  ( V  ∖  { 𝐷 } ) | 
						
							| 12 |  | fvres | ⊢ ( ( 𝐸 ‘ ndx )  ∈  ( V  ∖  { 𝐷 } )  →  ( ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) )  =  ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 13 | 11 12 | ax-mp | ⊢ ( ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) )  =  ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ‘ ( 𝐸 ‘ ndx ) ) | 
						
							| 14 |  | fvres | ⊢ ( ( 𝐸 ‘ ndx )  ∈  ( V  ∖  { 𝐷 } )  →  ( ( 𝑊  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) )  =  ( 𝑊 ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 15 | 11 14 | ax-mp | ⊢ ( ( 𝑊  ↾  ( V  ∖  { 𝐷 } ) ) ‘ ( 𝐸 ‘ ndx ) )  =  ( 𝑊 ‘ ( 𝐸 ‘ ndx ) ) | 
						
							| 16 | 8 13 15 | 3eqtr3g | ⊢ ( 𝑊  ∈  V  →  ( ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ‘ ( 𝐸 ‘ ndx ) )  =  ( 𝑊 ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 17 | 6 16 | eqtrid | ⊢ ( 𝑊  ∈  V  →  ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) )  =  ( 𝑊 ‘ ( 𝐸 ‘ ndx ) ) ) | 
						
							| 18 | 4 17 | eqtr4d | ⊢ ( 𝑊  ∈  V  →  ( 𝐸 ‘ 𝑊 )  =  ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ) ) | 
						
							| 19 | 1 | str0 | ⊢ ∅  =  ( 𝐸 ‘ ∅ ) | 
						
							| 20 |  | fvprc | ⊢ ( ¬  𝑊  ∈  V  →  ( 𝐸 ‘ 𝑊 )  =  ∅ ) | 
						
							| 21 |  | reldmsets | ⊢ Rel  dom   sSet | 
						
							| 22 | 21 | ovprc1 | ⊢ ( ¬  𝑊  ∈  V  →  ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 )  =  ∅ ) | 
						
							| 23 | 22 | fveq2d | ⊢ ( ¬  𝑊  ∈  V  →  ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) )  =  ( 𝐸 ‘ ∅ ) ) | 
						
							| 24 | 19 20 23 | 3eqtr4a | ⊢ ( ¬  𝑊  ∈  V  →  ( 𝐸 ‘ 𝑊 )  =  ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ) ) | 
						
							| 25 | 18 24 | pm2.61i | ⊢ ( 𝐸 ‘ 𝑊 )  =  ( 𝐸 ‘ ( 𝑊  sSet  〈 𝐷 ,  𝐶 〉 ) ) |