| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							simpr | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐴  ⊆  𝐵 )  | 
						
						
							| 2 | 
							
								
							 | 
							unss1 | 
							⊢ ( 𝐴  ⊆  𝐵  →  ( 𝐴  ∪  𝐶 )  ⊆  ( 𝐵  ∪  𝐶 ) )  | 
						
						
							| 3 | 
							
								
							 | 
							simpl1 | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐴  ∈   Sℋ  )  | 
						
						
							| 4 | 
							
								
							 | 
							shss | 
							⊢ ( 𝐴  ∈   Sℋ   →  𝐴  ⊆   ℋ )  | 
						
						
							| 5 | 
							
								3 4
							 | 
							syl | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐴  ⊆   ℋ )  | 
						
						
							| 6 | 
							
								
							 | 
							simpl3 | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐶  ∈   Sℋ  )  | 
						
						
							| 7 | 
							
								
							 | 
							shss | 
							⊢ ( 𝐶  ∈   Sℋ   →  𝐶  ⊆   ℋ )  | 
						
						
							| 8 | 
							
								6 7
							 | 
							syl | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐶  ⊆   ℋ )  | 
						
						
							| 9 | 
							
								5 8
							 | 
							unssd | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐴  ∪  𝐶 )  ⊆   ℋ )  | 
						
						
							| 10 | 
							
								
							 | 
							simpl2 | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐵  ∈   Sℋ  )  | 
						
						
							| 11 | 
							
								
							 | 
							shss | 
							⊢ ( 𝐵  ∈   Sℋ   →  𝐵  ⊆   ℋ )  | 
						
						
							| 12 | 
							
								10 11
							 | 
							syl | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  𝐵  ⊆   ℋ )  | 
						
						
							| 13 | 
							
								12 8
							 | 
							unssd | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐵  ∪  𝐶 )  ⊆   ℋ )  | 
						
						
							| 14 | 
							
								
							 | 
							occon2 | 
							⊢ ( ( ( 𝐴  ∪  𝐶 )  ⊆   ℋ  ∧  ( 𝐵  ∪  𝐶 )  ⊆   ℋ )  →  ( ( 𝐴  ∪  𝐶 )  ⊆  ( 𝐵  ∪  𝐶 )  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) ) )  | 
						
						
							| 15 | 
							
								9 13 14
							 | 
							syl2anc | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( ( 𝐴  ∪  𝐶 )  ⊆  ( 𝐵  ∪  𝐶 )  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) ) )  | 
						
						
							| 16 | 
							
								2 15
							 | 
							syl5 | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐴  ⊆  𝐵  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) ) )  | 
						
						
							| 17 | 
							
								1 16
							 | 
							mpd | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) )  | 
						
						
							| 18 | 
							
								
							 | 
							shjval | 
							⊢ ( ( 𝐴  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  →  ( 𝐴  ∨ℋ  𝐶 )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) ) )  | 
						
						
							| 19 | 
							
								3 6 18
							 | 
							syl2anc | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐴  ∨ℋ  𝐶 )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  𝐶 ) ) ) )  | 
						
						
							| 20 | 
							
								
							 | 
							shjval | 
							⊢ ( ( 𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  →  ( 𝐵  ∨ℋ  𝐶 )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) )  | 
						
						
							| 21 | 
							
								10 6 20
							 | 
							syl2anc | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐵  ∨ℋ  𝐶 )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐵  ∪  𝐶 ) ) ) )  | 
						
						
							| 22 | 
							
								17 19 21
							 | 
							3sstr4d | 
							⊢ ( ( ( 𝐴  ∈   Sℋ   ∧  𝐵  ∈   Sℋ   ∧  𝐶  ∈   Sℋ  )  ∧  𝐴  ⊆  𝐵 )  →  ( 𝐴  ∨ℋ  𝐶 )  ⊆  ( 𝐵  ∨ℋ  𝐶 ) )  |