public function testUnsionAssociative(Set $A, Set $B, Set $C) { $A∪⟮B∪C⟯ = $A->union($B->union($C)); $⟮A∪B⟯∪C = $A->union($B)->union($C); $this->assertEquals($A∪⟮B∪C⟯, $⟮A∪B⟯∪C); $this->assertEquals($A∪⟮B∪C⟯->asArray(), $⟮A∪B⟯∪C->asArray()); }