In this paper we will concentrate on the problem posed by Iberian Romance languages (i.e. Catalan, Portuguese, and Spanish), [...]
Eulàlia Bonet and Joan Mascaró, On the representation of contrasting rhotics, in: 1997, Fernando Martínez-Gil, Alfonso Morales-Front (eds.), Issues in the Phonology and Morphology of the Major Iberian Languages, p. 103ff., here p. 103