| 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 ) ) )  |