| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							osumcllem.l | 
							 |-  .<_ = ( le ` K )  | 
						
						
							| 2 | 
							
								
							 | 
							osumcllem.j | 
							 |-  .\/ = ( join ` K )  | 
						
						
							| 3 | 
							
								
							 | 
							osumcllem.a | 
							 |-  A = ( Atoms ` K )  | 
						
						
							| 4 | 
							
								
							 | 
							osumcllem.p | 
							 |-  .+ = ( +P ` K )  | 
						
						
							| 5 | 
							
								
							 | 
							osumcllem.o | 
							 |-  ._|_ = ( _|_P ` K )  | 
						
						
							| 6 | 
							
								
							 | 
							osumcllem.c | 
							 |-  C = ( PSubCl ` K )  | 
						
						
							| 7 | 
							
								
							 | 
							osumcllem.m | 
							 |-  M = ( X .+ { p } ) | 
						
						
							| 8 | 
							
								
							 | 
							osumcllem.u | 
							 |-  U = ( ._|_ ` ( ._|_ ` ( X .+ Y ) ) )  | 
						
						
							| 9 | 
							
								
							 | 
							simpl1 | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> K e. HL )  | 
						
						
							| 10 | 
							
								
							 | 
							simpl2 | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> X C_ A )  | 
						
						
							| 11 | 
							
								
							 | 
							simpr | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> p e. U )  | 
						
						
							| 12 | 
							
								11
							 | 
							snssd | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> { p } C_ U ) | 
						
						
							| 13 | 
							
								3 4
							 | 
							paddssat | 
							 |-  ( ( K e. HL /\ X C_ A /\ Y C_ A ) -> ( X .+ Y ) C_ A )  | 
						
						
							| 14 | 
							
								13
							 | 
							adantr | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> ( X .+ Y ) C_ A )  | 
						
						
							| 15 | 
							
								3 5
							 | 
							polssatN | 
							 |-  ( ( K e. HL /\ ( X .+ Y ) C_ A ) -> ( ._|_ ` ( X .+ Y ) ) C_ A )  | 
						
						
							| 16 | 
							
								9 14 15
							 | 
							syl2anc | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> ( ._|_ ` ( X .+ Y ) ) C_ A )  | 
						
						
							| 17 | 
							
								3 5
							 | 
							polssatN | 
							 |-  ( ( K e. HL /\ ( ._|_ ` ( X .+ Y ) ) C_ A ) -> ( ._|_ ` ( ._|_ ` ( X .+ Y ) ) ) C_ A )  | 
						
						
							| 18 | 
							
								9 16 17
							 | 
							syl2anc | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> ( ._|_ ` ( ._|_ ` ( X .+ Y ) ) ) C_ A )  | 
						
						
							| 19 | 
							
								8 18
							 | 
							eqsstrid | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> U C_ A )  | 
						
						
							| 20 | 
							
								12 19
							 | 
							sstrd | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> { p } C_ A ) | 
						
						
							| 21 | 
							
								3 4
							 | 
							sspadd1 | 
							 |-  ( ( K e. HL /\ X C_ A /\ { p } C_ A ) -> X C_ ( X .+ { p } ) ) | 
						
						
							| 22 | 
							
								9 10 20 21
							 | 
							syl3anc | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> X C_ ( X .+ { p } ) ) | 
						
						
							| 23 | 
							
								22 7
							 | 
							sseqtrrdi | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> X C_ M )  | 
						
						
							| 24 | 
							
								1 2 3 4 5 6 7 8
							 | 
							osumcllem1N | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> ( U i^i M ) = M )  | 
						
						
							| 25 | 
							
								23 24
							 | 
							sseqtrrd | 
							 |-  ( ( ( K e. HL /\ X C_ A /\ Y C_ A ) /\ p e. U ) -> X C_ ( U i^i M ) )  |