| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							paddfval.l | 
							⊢  ≤   =  ( le ‘ 𝐾 )  | 
						
						
							| 2 | 
							
								
							 | 
							paddfval.j | 
							⊢  ∨   =  ( join ‘ 𝐾 )  | 
						
						
							| 3 | 
							
								
							 | 
							paddfval.a | 
							⊢ 𝐴  =  ( Atoms ‘ 𝐾 )  | 
						
						
							| 4 | 
							
								
							 | 
							paddfval.p | 
							⊢  +   =  ( +𝑃 ‘ 𝐾 )  | 
						
						
							| 5 | 
							
								1 2 3 4
							 | 
							elpaddn0 | 
							⊢ ( ( ( 𝐾  ∈  Lat  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  ( 𝑋  ≠  ∅  ∧  𝑌  ≠  ∅ ) )  →  ( 𝑠  ∈  ( 𝑋  +  𝑌 )  ↔  ( 𝑠  ∈  𝐴  ∧  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑠  ≤  ( 𝑞  ∨  𝑟 ) ) ) )  | 
						
						
							| 6 | 
							
								
							 | 
							breq1 | 
							⊢ ( 𝑝  =  𝑠  →  ( 𝑝  ≤  ( 𝑞  ∨  𝑟 )  ↔  𝑠  ≤  ( 𝑞  ∨  𝑟 ) ) )  | 
						
						
							| 7 | 
							
								6
							 | 
							2rexbidv | 
							⊢ ( 𝑝  =  𝑠  →  ( ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑝  ≤  ( 𝑞  ∨  𝑟 )  ↔  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑠  ≤  ( 𝑞  ∨  𝑟 ) ) )  | 
						
						
							| 8 | 
							
								7
							 | 
							elrab | 
							⊢ ( 𝑠  ∈  { 𝑝  ∈  𝐴  ∣  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑝  ≤  ( 𝑞  ∨  𝑟 ) }  ↔  ( 𝑠  ∈  𝐴  ∧  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑠  ≤  ( 𝑞  ∨  𝑟 ) ) )  | 
						
						
							| 9 | 
							
								5 8
							 | 
							bitr4di | 
							⊢ ( ( ( 𝐾  ∈  Lat  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  ( 𝑋  ≠  ∅  ∧  𝑌  ≠  ∅ ) )  →  ( 𝑠  ∈  ( 𝑋  +  𝑌 )  ↔  𝑠  ∈  { 𝑝  ∈  𝐴  ∣  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑝  ≤  ( 𝑞  ∨  𝑟 ) } ) )  | 
						
						
							| 10 | 
							
								9
							 | 
							eqrdv | 
							⊢ ( ( ( 𝐾  ∈  Lat  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  ( 𝑋  ≠  ∅  ∧  𝑌  ≠  ∅ ) )  →  ( 𝑋  +  𝑌 )  =  { 𝑝  ∈  𝐴  ∣  ∃ 𝑞  ∈  𝑋 ∃ 𝑟  ∈  𝑌 𝑝  ≤  ( 𝑞  ∨  𝑟 ) } )  |