| Step | Hyp | Ref | Expression | 
						
							| 1 |  | psubclset.a | ⊢ 𝐴  =  ( Atoms ‘ 𝐾 ) | 
						
							| 2 |  | psubclset.p | ⊢  ⊥   =  ( ⊥𝑃 ‘ 𝐾 ) | 
						
							| 3 |  | psubclset.c | ⊢ 𝐶  =  ( PSubCl ‘ 𝐾 ) | 
						
							| 4 |  | elex | ⊢ ( 𝐾  ∈  𝐵  →  𝐾  ∈  V ) | 
						
							| 5 |  | fveq2 | ⊢ ( 𝑘  =  𝐾  →  ( Atoms ‘ 𝑘 )  =  ( Atoms ‘ 𝐾 ) ) | 
						
							| 6 | 5 1 | eqtr4di | ⊢ ( 𝑘  =  𝐾  →  ( Atoms ‘ 𝑘 )  =  𝐴 ) | 
						
							| 7 | 6 | sseq2d | ⊢ ( 𝑘  =  𝐾  →  ( 𝑠  ⊆  ( Atoms ‘ 𝑘 )  ↔  𝑠  ⊆  𝐴 ) ) | 
						
							| 8 |  | fveq2 | ⊢ ( 𝑘  =  𝐾  →  ( ⊥𝑃 ‘ 𝑘 )  =  ( ⊥𝑃 ‘ 𝐾 ) ) | 
						
							| 9 | 8 2 | eqtr4di | ⊢ ( 𝑘  =  𝐾  →  ( ⊥𝑃 ‘ 𝑘 )  =   ⊥  ) | 
						
							| 10 | 9 | fveq1d | ⊢ ( 𝑘  =  𝐾  →  ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 )  =  (  ⊥  ‘ 𝑠 ) ) | 
						
							| 11 | 9 10 | fveq12d | ⊢ ( 𝑘  =  𝐾  →  ( ( ⊥𝑃 ‘ 𝑘 ) ‘ ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 ) )  =  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) ) ) | 
						
							| 12 | 11 | eqeq1d | ⊢ ( 𝑘  =  𝐾  →  ( ( ( ⊥𝑃 ‘ 𝑘 ) ‘ ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 ) )  =  𝑠  ↔  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) ) | 
						
							| 13 | 7 12 | anbi12d | ⊢ ( 𝑘  =  𝐾  →  ( ( 𝑠  ⊆  ( Atoms ‘ 𝑘 )  ∧  ( ( ⊥𝑃 ‘ 𝑘 ) ‘ ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 ) )  =  𝑠 )  ↔  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) ) ) | 
						
							| 14 | 13 | abbidv | ⊢ ( 𝑘  =  𝐾  →  { 𝑠  ∣  ( 𝑠  ⊆  ( Atoms ‘ 𝑘 )  ∧  ( ( ⊥𝑃 ‘ 𝑘 ) ‘ ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 ) )  =  𝑠 ) }  =  { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) } ) | 
						
							| 15 |  | df-psubclN | ⊢ PSubCl  =  ( 𝑘  ∈  V  ↦  { 𝑠  ∣  ( 𝑠  ⊆  ( Atoms ‘ 𝑘 )  ∧  ( ( ⊥𝑃 ‘ 𝑘 ) ‘ ( ( ⊥𝑃 ‘ 𝑘 ) ‘ 𝑠 ) )  =  𝑠 ) } ) | 
						
							| 16 | 1 | fvexi | ⊢ 𝐴  ∈  V | 
						
							| 17 | 16 | pwex | ⊢ 𝒫  𝐴  ∈  V | 
						
							| 18 |  | velpw | ⊢ ( 𝑠  ∈  𝒫  𝐴  ↔  𝑠  ⊆  𝐴 ) | 
						
							| 19 | 18 | anbi1i | ⊢ ( ( 𝑠  ∈  𝒫  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 )  ↔  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) ) | 
						
							| 20 | 19 | abbii | ⊢ { 𝑠  ∣  ( 𝑠  ∈  𝒫  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) }  =  { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) } | 
						
							| 21 |  | ssab2 | ⊢ { 𝑠  ∣  ( 𝑠  ∈  𝒫  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) }  ⊆  𝒫  𝐴 | 
						
							| 22 | 20 21 | eqsstrri | ⊢ { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) }  ⊆  𝒫  𝐴 | 
						
							| 23 | 17 22 | ssexi | ⊢ { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) }  ∈  V | 
						
							| 24 | 14 15 23 | fvmpt | ⊢ ( 𝐾  ∈  V  →  ( PSubCl ‘ 𝐾 )  =  { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) } ) | 
						
							| 25 | 3 24 | eqtrid | ⊢ ( 𝐾  ∈  V  →  𝐶  =  { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) } ) | 
						
							| 26 | 4 25 | syl | ⊢ ( 𝐾  ∈  𝐵  →  𝐶  =  { 𝑠  ∣  ( 𝑠  ⊆  𝐴  ∧  (  ⊥  ‘ (  ⊥  ‘ 𝑠 ) )  =  𝑠 ) } ) |