1977 A. C. Foskett (ed. 3) vi. 81 When we have a thing defined by the material of which it is made, the thing precedes the material, which is introduced by the role operator.
2005 G. Flouris et al. in Y. Gil et al. 228 An additional advantage of the use of role operators..is the fact that they allow the definition of an axiom's negation.