This is an inofficial mirror of http://metamath.tirix.org for personal testing of a visualizer extension only.
Description: Lemma for paddass . The case when at least one sum argument is empty. (Contributed by NM, 12-Jan-2012)
| Ref | Expression | ||
|---|---|---|---|
| Hypotheses | paddass.a | ⊢ 𝐴 = ( Atoms ‘ 𝐾 ) | |
| paddass.p | ⊢ + = ( +𝑃 ‘ 𝐾 ) | ||
| Assertion | paddasslem17 | ⊢ ( ( 𝐾 ∈ HL ∧ ( 𝑋 ⊆ 𝐴 ∧ 𝑌 ⊆ 𝐴 ∧ 𝑍 ⊆ 𝐴 ) ∧ ¬ ( ( 𝑋 ≠ ∅ ∧ ( 𝑌 + 𝑍 ) ≠ ∅ ) ∧ ( 𝑌 ≠ ∅ ∧ 𝑍 ≠ ∅ ) ) ) → ( 𝑋 + ( 𝑌 + 𝑍 ) ) ⊆ ( ( 𝑋 + 𝑌 ) + 𝑍 ) ) |
| 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 ) ) |