| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							ocss | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ 𝐴 )  ⊆   ℋ )  | 
						
						
							| 2 | 
							
								
							 | 
							sshjval | 
							⊢ ( ( 𝐴  ⊆   ℋ  ∧  ( ⊥ ‘ 𝐴 )  ⊆   ℋ )  →  ( 𝐴  ∨ℋ  ( ⊥ ‘ 𝐴 ) )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) ) )  | 
						
						
							| 3 | 
							
								1 2
							 | 
							mpdan | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( 𝐴  ∨ℋ  ( ⊥ ‘ 𝐴 ) )  =  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) ) )  | 
						
						
							| 4 | 
							
								
							 | 
							ssun1 | 
							⊢ 𝐴  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  | 
						
						
							| 5 | 
							
								1
							 | 
							ancli | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( 𝐴  ⊆   ℋ  ∧  ( ⊥ ‘ 𝐴 )  ⊆   ℋ ) )  | 
						
						
							| 6 | 
							
								
							 | 
							unss | 
							⊢ ( ( 𝐴  ⊆   ℋ  ∧  ( ⊥ ‘ 𝐴 )  ⊆   ℋ )  ↔  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  ⊆   ℋ )  | 
						
						
							| 7 | 
							
								5 6
							 | 
							sylib | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  ⊆   ℋ )  | 
						
						
							| 8 | 
							
								
							 | 
							occon | 
							⊢ ( ( 𝐴  ⊆   ℋ  ∧  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  ⊆   ℋ )  →  ( 𝐴  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ 𝐴 ) ) )  | 
						
						
							| 9 | 
							
								7 8
							 | 
							mpdan | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( 𝐴  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ 𝐴 ) ) )  | 
						
						
							| 10 | 
							
								4 9
							 | 
							mpi | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ 𝐴 ) )  | 
						
						
							| 11 | 
							
								
							 | 
							ssun2 | 
							⊢ ( ⊥ ‘ 𝐴 )  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  | 
						
						
							| 12 | 
							
								
							 | 
							occon | 
							⊢ ( ( ( ⊥ ‘ 𝐴 )  ⊆   ℋ  ∧  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  ⊆   ℋ )  →  ( ( ⊥ ‘ 𝐴 )  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) ) )  | 
						
						
							| 13 | 
							
								1 7 12
							 | 
							syl2anc | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ( ⊥ ‘ 𝐴 )  ⊆  ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) ) )  | 
						
						
							| 14 | 
							
								11 13
							 | 
							mpi | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) )  | 
						
						
							| 15 | 
							
								10 14
							 | 
							ssind | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  ( ( ⊥ ‘ 𝐴 )  ∩  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) ) )  | 
						
						
							| 16 | 
							
								
							 | 
							ocsh | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ 𝐴 )  ∈   Sℋ  )  | 
						
						
							| 17 | 
							
								
							 | 
							ocin | 
							⊢ ( ( ⊥ ‘ 𝐴 )  ∈   Sℋ   →  ( ( ⊥ ‘ 𝐴 )  ∩  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) )  =  0ℋ )  | 
						
						
							| 18 | 
							
								16 17
							 | 
							syl | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ( ⊥ ‘ 𝐴 )  ∩  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) ) )  =  0ℋ )  | 
						
						
							| 19 | 
							
								15 18
							 | 
							sseqtrd | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ⊆  0ℋ )  | 
						
						
							| 20 | 
							
								
							 | 
							ocsh | 
							⊢ ( ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) )  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ∈   Sℋ  )  | 
						
						
							| 21 | 
							
								
							 | 
							sh0le | 
							⊢ ( ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  ∈   Sℋ   →  0ℋ  ⊆  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) )  | 
						
						
							| 22 | 
							
								7 20 21
							 | 
							3syl | 
							⊢ ( 𝐴  ⊆   ℋ  →  0ℋ  ⊆  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) )  | 
						
						
							| 23 | 
							
								19 22
							 | 
							eqssd | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) )  =  0ℋ )  | 
						
						
							| 24 | 
							
								23
							 | 
							fveq2d | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) )  =  ( ⊥ ‘ 0ℋ ) )  | 
						
						
							| 25 | 
							
								
							 | 
							choc0 | 
							⊢ ( ⊥ ‘ 0ℋ )  =   ℋ  | 
						
						
							| 26 | 
							
								24 25
							 | 
							eqtrdi | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( ⊥ ‘ ( ⊥ ‘ ( 𝐴  ∪  ( ⊥ ‘ 𝐴 ) ) ) )  =   ℋ )  | 
						
						
							| 27 | 
							
								3 26
							 | 
							eqtrd | 
							⊢ ( 𝐴  ⊆   ℋ  →  ( 𝐴  ∨ℋ  ( ⊥ ‘ 𝐴 ) )  =   ℋ )  |