| Step | Hyp | Ref | Expression | 
						
							| 1 |  | osum.1 |  |-  A e. CH | 
						
							| 2 |  | osum.2 |  |-  B e. CH | 
						
							| 3 | 1 2 | cmcm2i |  |-  ( A C_H B <-> A C_H ( _|_ ` B ) ) | 
						
							| 4 | 2 | choccli |  |-  ( _|_ ` B ) e. CH | 
						
							| 5 | 1 4 | cmbr4i |  |-  ( A C_H ( _|_ ` B ) <-> ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ ( _|_ ` B ) ) | 
						
							| 6 | 3 5 | bitri |  |-  ( A C_H B <-> ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ ( _|_ ` B ) ) | 
						
							| 7 | 1 | choccli |  |-  ( _|_ ` A ) e. CH | 
						
							| 8 | 7 4 | chjcli |  |-  ( ( _|_ ` A ) vH ( _|_ ` B ) ) e. CH | 
						
							| 9 | 1 8 | chincli |  |-  ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) e. CH | 
						
							| 10 | 9 2 | osumi |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ ( _|_ ` B ) -> ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) ) | 
						
							| 11 | 7 4 | chjcomi |  |-  ( ( _|_ ` A ) vH ( _|_ ` B ) ) = ( ( _|_ ` B ) vH ( _|_ ` A ) ) | 
						
							| 12 | 11 | ineq2i |  |-  ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) = ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) | 
						
							| 13 | 12 | oveq1i |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) = ( ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) vH B ) | 
						
							| 14 | 4 7 | chjcli |  |-  ( ( _|_ ` B ) vH ( _|_ ` A ) ) e. CH | 
						
							| 15 | 1 14 | chincli |  |-  ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) e. CH | 
						
							| 16 | 15 2 | chjcomi |  |-  ( ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) vH B ) = ( B vH ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) ) | 
						
							| 17 | 13 16 | eqtri |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) = ( B vH ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) ) | 
						
							| 18 | 2 1 | pjoml4i |  |-  ( B vH ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) ) = ( B vH A ) | 
						
							| 19 | 2 1 | chjcomi |  |-  ( B vH A ) = ( A vH B ) | 
						
							| 20 | 18 19 | eqtri |  |-  ( B vH ( A i^i ( ( _|_ ` B ) vH ( _|_ ` A ) ) ) ) = ( A vH B ) | 
						
							| 21 | 17 20 | eqtri |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) = ( A vH B ) | 
						
							| 22 | 21 | eqeq2i |  |-  ( ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) <-> ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( A vH B ) ) | 
						
							| 23 |  | inss1 |  |-  ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ A | 
						
							| 24 | 9 | chshii |  |-  ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) e. SH | 
						
							| 25 | 1 | chshii |  |-  A e. SH | 
						
							| 26 | 2 | chshii |  |-  B e. SH | 
						
							| 27 | 24 25 26 | shlessi |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ A -> ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) C_ ( A +H B ) ) | 
						
							| 28 | 23 27 | ax-mp |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) C_ ( A +H B ) | 
						
							| 29 |  | sseq1 |  |-  ( ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( A vH B ) -> ( ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) C_ ( A +H B ) <-> ( A vH B ) C_ ( A +H B ) ) ) | 
						
							| 30 | 28 29 | mpbii |  |-  ( ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( A vH B ) -> ( A vH B ) C_ ( A +H B ) ) | 
						
							| 31 | 22 30 | sylbi |  |-  ( ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) +H B ) = ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) vH B ) -> ( A vH B ) C_ ( A +H B ) ) | 
						
							| 32 | 10 31 | syl |  |-  ( ( A i^i ( ( _|_ ` A ) vH ( _|_ ` B ) ) ) C_ ( _|_ ` B ) -> ( A vH B ) C_ ( A +H B ) ) | 
						
							| 33 | 6 32 | sylbi |  |-  ( A C_H B -> ( A vH B ) C_ ( A +H B ) ) | 
						
							| 34 | 1 2 | chsleji |  |-  ( A +H B ) C_ ( A vH B ) | 
						
							| 35 | 33 34 | jctil |  |-  ( A C_H B -> ( ( A +H B ) C_ ( A vH B ) /\ ( A vH B ) C_ ( A +H B ) ) ) | 
						
							| 36 |  | eqss |  |-  ( ( A +H B ) = ( A vH B ) <-> ( ( A +H B ) C_ ( A vH B ) /\ ( A vH B ) C_ ( A +H B ) ) ) | 
						
							| 37 | 35 36 | sylibr |  |-  ( A C_H B -> ( A +H B ) = ( A vH B ) ) |