“…Finding a forbidden subgraph characterization of circular-arc graphs is a challenging open problem studied since the late 1960s [14,21,22,23,24]. Many partial results toward this goal have been proposed over the years, but a full answer remains elusive, capturing the interest of many researchers [1,2,6,14,17,21,22,23,24]. A certifying algorithm is an algorithm that outputs a certificate, along with its answer (be it positive or negative), where the certificate can be used to easily justify the given answer.…”