  An interval graph is the intersection graph of a finite set of intervals on a
line and a circular-arc graph is the intersection graph of a finite set of arcs
on a circle. While a forbidden induced subgraph characterization of interval
graphs was found fifty years ago, finding an analogous characterization for
circular-arc graphs is a long-standing open problem. In this work, we study the
intersection graphs of finite sets of arcs on a circle no three of which cover
the circle, known as normal Helly circular-arc graphs. Those circular-arc
graphs which are minimal forbidden induced subgraphs for the class of normal
Helly circular-arc graphs were identified by Lin, Soulignac, and Szwarcfiter,
who also posed the problem of determining the remaining minimal forbidden
induced subgraphs. In this work, we solve their problem, obtaining the complete
list of minimal forbidden induced subgraphs for the class of normal Helly
circular-arc graphs.
