| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							paddass.a | 
							⊢ 𝐴  =  ( Atoms ‘ 𝐾 )  | 
						
						
							| 2 | 
							
								
							 | 
							paddass.p | 
							⊢  +   =  ( +𝑃 ‘ 𝐾 )  | 
						
						
							| 3 | 
							
								
							 | 
							ianor | 
							⊢ ( ¬  ( ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∧  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) )  ↔  ( ¬  ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∨  ¬  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) ) )  | 
						
						
							| 4 | 
							
								
							 | 
							ianor | 
							⊢ ( ¬  ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ↔  ( ¬  𝑋  ≠  ∅  ∨  ¬  ( 𝑌  +  𝑍 )  ≠  ∅ ) )  | 
						
						
							| 5 | 
							
								
							 | 
							nne | 
							⊢ ( ¬  𝑋  ≠  ∅  ↔  𝑋  =  ∅ )  | 
						
						
							| 6 | 
							
								
							 | 
							nne | 
							⊢ ( ¬  ( 𝑌  +  𝑍 )  ≠  ∅  ↔  ( 𝑌  +  𝑍 )  =  ∅ )  | 
						
						
							| 7 | 
							
								5 6
							 | 
							orbi12i | 
							⊢ ( ( ¬  𝑋  ≠  ∅  ∨  ¬  ( 𝑌  +  𝑍 )  ≠  ∅ )  ↔  ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ ) )  | 
						
						
							| 8 | 
							
								4 7
							 | 
							bitri | 
							⊢ ( ¬  ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ↔  ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ ) )  | 
						
						
							| 9 | 
							
								
							 | 
							ianor | 
							⊢ ( ¬  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ )  ↔  ( ¬  𝑌  ≠  ∅  ∨  ¬  𝑍  ≠  ∅ ) )  | 
						
						
							| 10 | 
							
								
							 | 
							nne | 
							⊢ ( ¬  𝑌  ≠  ∅  ↔  𝑌  =  ∅ )  | 
						
						
							| 11 | 
							
								
							 | 
							nne | 
							⊢ ( ¬  𝑍  ≠  ∅  ↔  𝑍  =  ∅ )  | 
						
						
							| 12 | 
							
								10 11
							 | 
							orbi12i | 
							⊢ ( ( ¬  𝑌  ≠  ∅  ∨  ¬  𝑍  ≠  ∅ )  ↔  ( 𝑌  =  ∅  ∨  𝑍  =  ∅ ) )  | 
						
						
							| 13 | 
							
								9 12
							 | 
							bitri | 
							⊢ ( ¬  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ )  ↔  ( 𝑌  =  ∅  ∨  𝑍  =  ∅ ) )  | 
						
						
							| 14 | 
							
								8 13
							 | 
							orbi12i | 
							⊢ ( ( ¬  ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∨  ¬  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) )  ↔  ( ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ )  ∨  ( 𝑌  =  ∅  ∨  𝑍  =  ∅ ) ) )  | 
						
						
							| 15 | 
							
								3 14
							 | 
							bitri | 
							⊢ ( ¬  ( ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∧  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) )  ↔  ( ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ )  ∨  ( 𝑌  =  ∅  ∨  𝑍  =  ∅ ) ) )  | 
						
						
							| 16 | 
							
								1 2
							 | 
							paddssat | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 )  →  ( 𝑌  +  𝑍 )  ⊆  𝐴 )  | 
						
						
							| 17 | 
							
								16
							 | 
							3adant3r1 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑌  +  𝑍 )  ⊆  𝐴 )  | 
						
						
							| 18 | 
							
								1 2
							 | 
							padd02 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑌  +  𝑍 )  ⊆  𝐴 )  →  ( ∅  +  ( 𝑌  +  𝑍 ) )  =  ( 𝑌  +  𝑍 ) )  | 
						
						
							| 19 | 
							
								17 18
							 | 
							syldan | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ∅  +  ( 𝑌  +  𝑍 ) )  =  ( 𝑌  +  𝑍 ) )  | 
						
						
							| 20 | 
							
								1 2
							 | 
							padd02 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑌  ⊆  𝐴 )  →  ( ∅  +  𝑌 )  =  𝑌 )  | 
						
						
							| 21 | 
							
								20
							 | 
							3ad2antr2 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ∅  +  𝑌 )  =  𝑌 )  | 
						
						
							| 22 | 
							
								21
							 | 
							oveq1d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( ∅  +  𝑌 )  +  𝑍 )  =  ( 𝑌  +  𝑍 ) )  | 
						
						
							| 23 | 
							
								19 22
							 | 
							eqtr4d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ∅  +  ( 𝑌  +  𝑍 ) )  =  ( ( ∅  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 24 | 
							
								
							 | 
							oveq1 | 
							⊢ ( 𝑋  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ∅  +  ( 𝑌  +  𝑍 ) ) )  | 
						
						
							| 25 | 
							
								
							 | 
							oveq1 | 
							⊢ ( 𝑋  =  ∅  →  ( 𝑋  +  𝑌 )  =  ( ∅  +  𝑌 ) )  | 
						
						
							| 26 | 
							
								25
							 | 
							oveq1d | 
							⊢ ( 𝑋  =  ∅  →  ( ( 𝑋  +  𝑌 )  +  𝑍 )  =  ( ( ∅  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 27 | 
							
								24 26
							 | 
							eqeq12d | 
							⊢ ( 𝑋  =  ∅  →  ( ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 )  ↔  ( ∅  +  ( 𝑌  +  𝑍 ) )  =  ( ( ∅  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 28 | 
							
								23 27
							 | 
							syl5ibrcom | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 29 | 
							
								
							 | 
							eqimss | 
							⊢ ( ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 30 | 
							
								28 29
							 | 
							syl6 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 31 | 
							
								1 2
							 | 
							padd01 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴 )  →  ( 𝑋  +  ∅ )  =  𝑋 )  | 
						
						
							| 32 | 
							
								31
							 | 
							3ad2antr1 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ∅ )  =  𝑋 )  | 
						
						
							| 33 | 
							
								1 2
							 | 
							sspadd1 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  →  𝑋  ⊆  ( 𝑋  +  𝑌 ) )  | 
						
						
							| 34 | 
							
								33
							 | 
							3adant3r3 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  𝑋  ⊆  ( 𝑋  +  𝑌 ) )  | 
						
						
							| 35 | 
							
								
							 | 
							simpl | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  𝐾  ∈  HL )  | 
						
						
							| 36 | 
							
								1 2
							 | 
							paddssat | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴 )  →  ( 𝑋  +  𝑌 )  ⊆  𝐴 )  | 
						
						
							| 37 | 
							
								36
							 | 
							3adant3r3 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  𝑌 )  ⊆  𝐴 )  | 
						
						
							| 38 | 
							
								
							 | 
							simpr3 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  𝑍  ⊆  𝐴 )  | 
						
						
							| 39 | 
							
								1 2
							 | 
							sspadd1 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  +  𝑌 )  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 )  →  ( 𝑋  +  𝑌 )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 40 | 
							
								35 37 38 39
							 | 
							syl3anc | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  𝑌 )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 41 | 
							
								34 40
							 | 
							sstrd | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  𝑋  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 42 | 
							
								32 41
							 | 
							eqsstrd | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ∅ )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  | 
						
						
							| 43 | 
							
								
							 | 
							oveq2 | 
							⊢ ( ( 𝑌  +  𝑍 )  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( 𝑋  +  ∅ ) )  | 
						
						
							| 44 | 
							
								43
							 | 
							sseq1d | 
							⊢ ( ( 𝑌  +  𝑍 )  =  ∅  →  ( ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 )  ↔  ( 𝑋  +  ∅ )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 45 | 
							
								42 44
							 | 
							syl5ibrcom | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑌  +  𝑍 )  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 46 | 
							
								30 45
							 | 
							jaod | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 47 | 
							
								1 2
							 | 
							padd02 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑍  ⊆  𝐴 )  →  ( ∅  +  𝑍 )  =  𝑍 )  | 
						
						
							| 48 | 
							
								47
							 | 
							3ad2antr3 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ∅  +  𝑍 )  =  𝑍 )  | 
						
						
							| 49 | 
							
								48
							 | 
							oveq2d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ( ∅  +  𝑍 ) )  =  ( 𝑋  +  𝑍 ) )  | 
						
						
							| 50 | 
							
								32
							 | 
							oveq1d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑋  +  ∅ )  +  𝑍 )  =  ( 𝑋  +  𝑍 ) )  | 
						
						
							| 51 | 
							
								49 50
							 | 
							eqtr4d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ( ∅  +  𝑍 ) )  =  ( ( 𝑋  +  ∅ )  +  𝑍 ) )  | 
						
						
							| 52 | 
							
								
							 | 
							oveq1 | 
							⊢ ( 𝑌  =  ∅  →  ( 𝑌  +  𝑍 )  =  ( ∅  +  𝑍 ) )  | 
						
						
							| 53 | 
							
								52
							 | 
							oveq2d | 
							⊢ ( 𝑌  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( 𝑋  +  ( ∅  +  𝑍 ) ) )  | 
						
						
							| 54 | 
							
								
							 | 
							oveq2 | 
							⊢ ( 𝑌  =  ∅  →  ( 𝑋  +  𝑌 )  =  ( 𝑋  +  ∅ ) )  | 
						
						
							| 55 | 
							
								54
							 | 
							oveq1d | 
							⊢ ( 𝑌  =  ∅  →  ( ( 𝑋  +  𝑌 )  +  𝑍 )  =  ( ( 𝑋  +  ∅ )  +  𝑍 ) )  | 
						
						
							| 56 | 
							
								53 55
							 | 
							eqeq12d | 
							⊢ ( 𝑌  =  ∅  →  ( ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 )  ↔  ( 𝑋  +  ( ∅  +  𝑍 ) )  =  ( ( 𝑋  +  ∅ )  +  𝑍 ) ) )  | 
						
						
							| 57 | 
							
								51 56
							 | 
							syl5ibrcom | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑌  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 58 | 
							
								1 2
							 | 
							padd01 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  𝑌  ⊆  𝐴 )  →  ( 𝑌  +  ∅ )  =  𝑌 )  | 
						
						
							| 59 | 
							
								58
							 | 
							3ad2antr2 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑌  +  ∅ )  =  𝑌 )  | 
						
						
							| 60 | 
							
								59
							 | 
							oveq2d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ( 𝑌  +  ∅ ) )  =  ( 𝑋  +  𝑌 ) )  | 
						
						
							| 61 | 
							
								1 2
							 | 
							padd01 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  +  𝑌 )  ⊆  𝐴 )  →  ( ( 𝑋  +  𝑌 )  +  ∅ )  =  ( 𝑋  +  𝑌 ) )  | 
						
						
							| 62 | 
							
								37 61
							 | 
							syldan | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑋  +  𝑌 )  +  ∅ )  =  ( 𝑋  +  𝑌 ) )  | 
						
						
							| 63 | 
							
								60 62
							 | 
							eqtr4d | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑋  +  ( 𝑌  +  ∅ ) )  =  ( ( 𝑋  +  𝑌 )  +  ∅ ) )  | 
						
						
							| 64 | 
							
								
							 | 
							oveq2 | 
							⊢ ( 𝑍  =  ∅  →  ( 𝑌  +  𝑍 )  =  ( 𝑌  +  ∅ ) )  | 
						
						
							| 65 | 
							
								64
							 | 
							oveq2d | 
							⊢ ( 𝑍  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( 𝑋  +  ( 𝑌  +  ∅ ) ) )  | 
						
						
							| 66 | 
							
								
							 | 
							oveq2 | 
							⊢ ( 𝑍  =  ∅  →  ( ( 𝑋  +  𝑌 )  +  𝑍 )  =  ( ( 𝑋  +  𝑌 )  +  ∅ ) )  | 
						
						
							| 67 | 
							
								65 66
							 | 
							eqeq12d | 
							⊢ ( 𝑍  =  ∅  →  ( ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 )  ↔  ( 𝑋  +  ( 𝑌  +  ∅ ) )  =  ( ( 𝑋  +  𝑌 )  +  ∅ ) ) )  | 
						
						
							| 68 | 
							
								63 67
							 | 
							syl5ibrcom | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( 𝑍  =  ∅  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 69 | 
							
								57 68
							 | 
							jaod | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑌  =  ∅  ∨  𝑍  =  ∅ )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  =  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 70 | 
							
								69 29
							 | 
							syl6 | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( 𝑌  =  ∅  ∨  𝑍  =  ∅ )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 71 | 
							
								46 70
							 | 
							jaod | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ( ( 𝑋  =  ∅  ∨  ( 𝑌  +  𝑍 )  =  ∅ )  ∨  ( 𝑌  =  ∅  ∨  𝑍  =  ∅ ) )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 72 | 
							
								15 71
							 | 
							biimtrid | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 ) )  →  ( ¬  ( ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∧  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) ) )  | 
						
						
							| 73 | 
							
								72
							 | 
							3impia | 
							⊢ ( ( 𝐾  ∈  HL  ∧  ( 𝑋  ⊆  𝐴  ∧  𝑌  ⊆  𝐴  ∧  𝑍  ⊆  𝐴 )  ∧  ¬  ( ( 𝑋  ≠  ∅  ∧  ( 𝑌  +  𝑍 )  ≠  ∅ )  ∧  ( 𝑌  ≠  ∅  ∧  𝑍  ≠  ∅ ) ) )  →  ( 𝑋  +  ( 𝑌  +  𝑍 ) )  ⊆  ( ( 𝑋  +  𝑌 )  +  𝑍 ) )  |