“Anchovies Dream of an Olive Mausoleum” is the subtitle Chus Martínez has given to “Idiosyncrasy,” her new arrangement of the Helga de Alvear Foundation’s collection of work from the second half of the twentieth century, assembled over 50 years by the Madrid-based German-Spanish gallerist. By locating the foundation in the historic city of Cáceres and annually inviting external curators to propose new displays and hangings of the collection, Helga de Alvear is also offering it up as a laboratory, an experimental field where new ideas can be tried and tested. Martínez takes full advantage of the occasion, starting with the show’s subtitle, which bears a clear statement. For there are two things fans of tapas (and Spanish art) should know: one, that in Spain popular refinement demands that olives, since time immemorial, be filled with anchovies at aperitivo time; and two, that this quote comes from Ramón Gómez de la Serna, or simply “Ramón,” the spiritual leader of Iberian surrealism, and a kind of Breton of the Spanish avant-garde. This is one of his “greguerías,” an untranslatable phrase coined by Ramón himself to describe the utterances which extract new meanings from unexpectedly juxtaposed words and ideas. And it’s precisely this game …