| Step | Hyp | Ref | Expression | 
						
							| 1 |  | mdslle1.1 | ⊢ 𝐴  ∈   Cℋ | 
						
							| 2 |  | mdslle1.2 | ⊢ 𝐵  ∈   Cℋ | 
						
							| 3 |  | mdslle1.3 | ⊢ 𝐶  ∈   Cℋ | 
						
							| 4 |  | mdslle1.4 | ⊢ 𝐷  ∈   Cℋ | 
						
							| 5 | 3 4 1 | chlej1i | ⊢ ( 𝐶  ⊆  𝐷  →  ( 𝐶  ∨ℋ  𝐴 )  ⊆  ( 𝐷  ∨ℋ  𝐴 ) ) | 
						
							| 6 |  | ssrin | ⊢ ( ( 𝐶  ∨ℋ  𝐴 )  ⊆  ( 𝐷  ∨ℋ  𝐴 )  →  ( ( 𝐶  ∨ℋ  𝐴 )  ∩  𝐵 )  ⊆  ( ( 𝐷  ∨ℋ  𝐴 )  ∩  𝐵 ) ) | 
						
							| 7 |  | id | ⊢ ( 𝐴  𝑀ℋ  𝐵  →  𝐴  𝑀ℋ  𝐵 ) | 
						
							| 8 |  | ssin | ⊢ ( ( ( 𝐴  ∩  𝐵 )  ⊆  𝐶  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐷 )  ↔  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 ) ) | 
						
							| 9 | 8 | bicomi | ⊢ ( ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ↔  ( ( 𝐴  ∩  𝐵 )  ⊆  𝐶  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐷 ) ) | 
						
							| 10 | 9 | simplbi | ⊢ ( ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  →  ( 𝐴  ∩  𝐵 )  ⊆  𝐶 ) | 
						
							| 11 | 3 4 2 | chlubi | ⊢ ( ( 𝐶  ⊆  𝐵  ∧  𝐷  ⊆  𝐵 )  ↔  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 ) | 
						
							| 12 | 11 | bicomi | ⊢ ( ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵  ↔  ( 𝐶  ⊆  𝐵  ∧  𝐷  ⊆  𝐵 ) ) | 
						
							| 13 | 12 | simplbi | ⊢ ( ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵  →  𝐶  ⊆  𝐵 ) | 
						
							| 14 | 1 2 3 | 3pm3.2i | ⊢ ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐶  ∈   Cℋ  ) | 
						
							| 15 |  | mdsl3 | ⊢ ( ( ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐶  ∈   Cℋ  )  ∧  ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐶  ∧  𝐶  ⊆  𝐵 ) )  →  ( ( 𝐶  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐶 ) | 
						
							| 16 | 14 15 | mpan | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐶  ∧  𝐶  ⊆  𝐵 )  →  ( ( 𝐶  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐶 ) | 
						
							| 17 | 7 10 13 16 | syl3an | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ∧  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 )  →  ( ( 𝐶  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐶 ) | 
						
							| 18 | 9 | simprbi | ⊢ ( ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  →  ( 𝐴  ∩  𝐵 )  ⊆  𝐷 ) | 
						
							| 19 | 12 | simprbi | ⊢ ( ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵  →  𝐷  ⊆  𝐵 ) | 
						
							| 20 | 1 2 4 | 3pm3.2i | ⊢ ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐷  ∈   Cℋ  ) | 
						
							| 21 |  | mdsl3 | ⊢ ( ( ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐷  ∈   Cℋ  )  ∧  ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐷  ∧  𝐷  ⊆  𝐵 ) )  →  ( ( 𝐷  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐷 ) | 
						
							| 22 | 20 21 | mpan | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  𝐷  ∧  𝐷  ⊆  𝐵 )  →  ( ( 𝐷  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐷 ) | 
						
							| 23 | 7 18 19 22 | syl3an | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ∧  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 )  →  ( ( 𝐷  ∨ℋ  𝐴 )  ∩  𝐵 )  =  𝐷 ) | 
						
							| 24 | 17 23 | sseq12d | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ∧  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 )  →  ( ( ( 𝐶  ∨ℋ  𝐴 )  ∩  𝐵 )  ⊆  ( ( 𝐷  ∨ℋ  𝐴 )  ∩  𝐵 )  ↔  𝐶  ⊆  𝐷 ) ) | 
						
							| 25 | 6 24 | imbitrid | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ∧  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 )  →  ( ( 𝐶  ∨ℋ  𝐴 )  ⊆  ( 𝐷  ∨ℋ  𝐴 )  →  𝐶  ⊆  𝐷 ) ) | 
						
							| 26 | 5 25 | impbid2 | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  ( 𝐴  ∩  𝐵 )  ⊆  ( 𝐶  ∩  𝐷 )  ∧  ( 𝐶  ∨ℋ  𝐷 )  ⊆  𝐵 )  →  ( 𝐶  ⊆  𝐷  ↔  ( 𝐶  ∨ℋ  𝐴 )  ⊆  ( 𝐷  ∨ℋ  𝐴 ) ) ) |