This is a strange sort of retrospective. “Un certo numero di cose” (A Certain Number of Things) covers the whole span of Cesare Pietroiusti’s life so far, with one of the titular “things” for every year from his birth in 1955 up through 2019, when the show opened. Thus the exhibition, curated by Lorenzo Balbi with Sabrina Samorì, includes items related to the artist’s childhood and adolescence: report cards, family photographs, letters to Santa Claus, everyday objects. Pietroiusti’s intention was to include works—if that’s what they are—of indeterminate status, suspended between art and non-art,