| Step | Hyp | Ref | Expression | 
						
							| 1 |  | osumcllem.l | ⊢  ≤   =  ( le ‘ 𝐾 ) | 
						
							| 2 |  | osumcllem.j | ⊢  ∨   =  ( join ‘ 𝐾 ) | 
						
							| 3 |  | osumcllem.a | ⊢ 𝐴  =  ( Atoms ‘ 𝐾 ) | 
						
							| 4 |  | osumcllem.p | ⊢  +   =  ( +𝑃 ‘ 𝐾 ) | 
						
							| 5 |  | osumcllem.o | ⊢  ⊥   =  ( ⊥𝑃 ‘ 𝐾 ) | 
						
							| 6 |  | osumcllem.c | ⊢ 𝐶  =  ( PSubCl ‘ 𝐾 ) | 
						
							| 7 |  | osumcllem.m | ⊢ 𝑀  =  ( 𝑋  +  { 𝑝 } ) | 
						
							| 8 |  | osumcllem.u | ⊢ 𝑈  =  (  ⊥  ‘ (  ⊥  ‘ ( 𝑋  +  𝑌 ) ) ) | 
						
							| 9 |  | simp11 | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝐾  ∈  HL ) | 
						
							| 10 |  | simp2 | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑝  ∈  𝐴 ) | 
						
							| 11 | 10 | snssd | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  { 𝑝 }  ⊆  𝐴 ) | 
						
							| 12 |  | simp12 | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑋  ⊆  𝐴 ) | 
						
							| 13 | 3 4 | sspadd2 | ⊢ ( ( 𝐾  ∈  HL  ∧  { 𝑝 }  ⊆  𝐴  ∧  𝑋  ⊆  𝐴 )  →  { 𝑝 }  ⊆  ( 𝑋  +  { 𝑝 } ) ) | 
						
							| 14 | 9 11 12 13 | syl3anc | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  { 𝑝 }  ⊆  ( 𝑋  +  { 𝑝 } ) ) | 
						
							| 15 |  | vex | ⊢ 𝑝  ∈  V | 
						
							| 16 | 15 | snss | ⊢ ( 𝑝  ∈  ( 𝑋  +  { 𝑝 } )  ↔  { 𝑝 }  ⊆  ( 𝑋  +  { 𝑝 } ) ) | 
						
							| 17 | 14 16 | sylibr | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑝  ∈  ( 𝑋  +  { 𝑝 } ) ) | 
						
							| 18 | 17 7 | eleqtrrdi | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑝  ∈  𝑀 ) | 
						
							| 19 | 3 4 | sspadd1 | ⊢ ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  →  𝑋  ⊆  ( 𝑋  +  𝑌 ) ) | 
						
							| 20 | 19 | 3ad2ant1 | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑋  ⊆  ( 𝑋  +  𝑌 ) ) | 
						
							| 21 |  | simp3 | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) ) | 
						
							| 22 | 20 21 | ssneldd | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  ¬  𝑝  ∈  𝑋 ) | 
						
							| 23 |  | nelne1 | ⊢ ( ( 𝑝  ∈  𝑀  ∧  ¬  𝑝  ∈  𝑋 )  →  𝑀  ≠  𝑋 ) | 
						
							| 24 | 18 22 23 | syl2anc | ⊢ ( ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  ∧  𝑝  ∈  𝐴  ∧  ¬  𝑝  ∈  ( 𝑋  +  𝑌 ) )  →  𝑀  ≠  𝑋 ) |