 As regards the mereology-friendly strategy, it has been suggested that structural properties actually include extra components accounting for structures, so that the Principle of Uniqueness of Composition is safe. Considering methane, Pagès (2002) claims that such a structural property is composed of the properties carbon and hydrogen, a bonding relation and a peculiar first-order, formal relation between the atoms. According to Kalhat (2008), the extra component is a second-order arrangement relation between the first-order properties. Ordering formal relations—together with causally individuated properties—are also invoked by McFarland (2018).