| Step | Hyp | Ref | Expression | 
						
							| 1 |  | mdsym.1 | ⊢ 𝐴  ∈   Cℋ | 
						
							| 2 |  | mdsym.2 | ⊢ 𝐵  ∈   Cℋ | 
						
							| 3 | 2 | choccli | ⊢ ( ⊥ ‘ 𝐵 )  ∈   Cℋ | 
						
							| 4 | 1 | choccli | ⊢ ( ⊥ ‘ 𝐴 )  ∈   Cℋ | 
						
							| 5 |  | eqid | ⊢ ( ( ⊥ ‘ 𝐵 )  ∨ℋ  𝑥 )  =  ( ( ⊥ ‘ 𝐵 )  ∨ℋ  𝑥 ) | 
						
							| 6 | 3 4 5 | mdsymlem8 | ⊢ ( ( ( ⊥ ‘ 𝐵 )  ≠  0ℋ  ∧  ( ⊥ ‘ 𝐴 )  ≠  0ℋ )  →  ( ( ⊥ ‘ 𝐴 )  𝑀ℋ*  ( ⊥ ‘ 𝐵 )  ↔  ( ⊥ ‘ 𝐵 )  𝑀ℋ*  ( ⊥ ‘ 𝐴 ) ) ) | 
						
							| 7 |  | mddmd | ⊢ ( ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ  )  →  ( 𝐴  𝑀ℋ  𝐵  ↔  ( ⊥ ‘ 𝐴 )  𝑀ℋ*  ( ⊥ ‘ 𝐵 ) ) ) | 
						
							| 8 | 1 2 7 | mp2an | ⊢ ( 𝐴  𝑀ℋ  𝐵  ↔  ( ⊥ ‘ 𝐴 )  𝑀ℋ*  ( ⊥ ‘ 𝐵 ) ) | 
						
							| 9 |  | mddmd | ⊢ ( ( 𝐵  ∈   Cℋ   ∧  𝐴  ∈   Cℋ  )  →  ( 𝐵  𝑀ℋ  𝐴  ↔  ( ⊥ ‘ 𝐵 )  𝑀ℋ*  ( ⊥ ‘ 𝐴 ) ) ) | 
						
							| 10 | 2 1 9 | mp2an | ⊢ ( 𝐵  𝑀ℋ  𝐴  ↔  ( ⊥ ‘ 𝐵 )  𝑀ℋ*  ( ⊥ ‘ 𝐴 ) ) | 
						
							| 11 | 6 8 10 | 3bitr4g | ⊢ ( ( ( ⊥ ‘ 𝐵 )  ≠  0ℋ  ∧  ( ⊥ ‘ 𝐴 )  ≠  0ℋ )  →  ( 𝐴  𝑀ℋ  𝐵  ↔  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 12 | 1 | chssii | ⊢ 𝐴  ⊆   ℋ | 
						
							| 13 |  | fveq2 | ⊢ ( ( ⊥ ‘ 𝐵 )  =  0ℋ  →  ( ⊥ ‘ ( ⊥ ‘ 𝐵 ) )  =  ( ⊥ ‘ 0ℋ ) ) | 
						
							| 14 | 2 | pjococi | ⊢ ( ⊥ ‘ ( ⊥ ‘ 𝐵 ) )  =  𝐵 | 
						
							| 15 |  | choc0 | ⊢ ( ⊥ ‘ 0ℋ )  =   ℋ | 
						
							| 16 | 13 14 15 | 3eqtr3g | ⊢ ( ( ⊥ ‘ 𝐵 )  =  0ℋ  →  𝐵  =   ℋ ) | 
						
							| 17 | 12 16 | sseqtrrid | ⊢ ( ( ⊥ ‘ 𝐵 )  =  0ℋ  →  𝐴  ⊆  𝐵 ) | 
						
							| 18 |  | ssmd1 | ⊢ ( ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐴  ⊆  𝐵 )  →  𝐴  𝑀ℋ  𝐵 ) | 
						
							| 19 | 1 2 18 | mp3an12 | ⊢ ( 𝐴  ⊆  𝐵  →  𝐴  𝑀ℋ  𝐵 ) | 
						
							| 20 |  | ssmd2 | ⊢ ( ( 𝐴  ∈   Cℋ   ∧  𝐵  ∈   Cℋ   ∧  𝐴  ⊆  𝐵 )  →  𝐵  𝑀ℋ  𝐴 ) | 
						
							| 21 | 1 2 20 | mp3an12 | ⊢ ( 𝐴  ⊆  𝐵  →  𝐵  𝑀ℋ  𝐴 ) | 
						
							| 22 | 19 21 | jca | ⊢ ( 𝐴  ⊆  𝐵  →  ( 𝐴  𝑀ℋ  𝐵  ∧  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 23 |  | pm5.1 | ⊢ ( ( 𝐴  𝑀ℋ  𝐵  ∧  𝐵  𝑀ℋ  𝐴 )  →  ( 𝐴  𝑀ℋ  𝐵  ↔  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 24 | 17 22 23 | 3syl | ⊢ ( ( ⊥ ‘ 𝐵 )  =  0ℋ  →  ( 𝐴  𝑀ℋ  𝐵  ↔  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 25 | 2 | chssii | ⊢ 𝐵  ⊆   ℋ | 
						
							| 26 |  | fveq2 | ⊢ ( ( ⊥ ‘ 𝐴 )  =  0ℋ  →  ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) )  =  ( ⊥ ‘ 0ℋ ) ) | 
						
							| 27 | 1 | pjococi | ⊢ ( ⊥ ‘ ( ⊥ ‘ 𝐴 ) )  =  𝐴 | 
						
							| 28 | 26 27 15 | 3eqtr3g | ⊢ ( ( ⊥ ‘ 𝐴 )  =  0ℋ  →  𝐴  =   ℋ ) | 
						
							| 29 | 25 28 | sseqtrrid | ⊢ ( ( ⊥ ‘ 𝐴 )  =  0ℋ  →  𝐵  ⊆  𝐴 ) | 
						
							| 30 |  | ssmd2 | ⊢ ( ( 𝐵  ∈   Cℋ   ∧  𝐴  ∈   Cℋ   ∧  𝐵  ⊆  𝐴 )  →  𝐴  𝑀ℋ  𝐵 ) | 
						
							| 31 | 2 1 30 | mp3an12 | ⊢ ( 𝐵  ⊆  𝐴  →  𝐴  𝑀ℋ  𝐵 ) | 
						
							| 32 |  | ssmd1 | ⊢ ( ( 𝐵  ∈   Cℋ   ∧  𝐴  ∈   Cℋ   ∧  𝐵  ⊆  𝐴 )  →  𝐵  𝑀ℋ  𝐴 ) | 
						
							| 33 | 2 1 32 | mp3an12 | ⊢ ( 𝐵  ⊆  𝐴  →  𝐵  𝑀ℋ  𝐴 ) | 
						
							| 34 | 31 33 | jca | ⊢ ( 𝐵  ⊆  𝐴  →  ( 𝐴  𝑀ℋ  𝐵  ∧  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 35 | 29 34 23 | 3syl | ⊢ ( ( ⊥ ‘ 𝐴 )  =  0ℋ  →  ( 𝐴  𝑀ℋ  𝐵  ↔  𝐵  𝑀ℋ  𝐴 ) ) | 
						
							| 36 | 11 24 35 | pm2.61iine | ⊢ ( 𝐴  𝑀ℋ  𝐵  ↔  𝐵  𝑀ℋ  𝐴 ) |