Judith Mackrell: “In classical ballet, casting can be everything. In modern dance, performances are no less individual, but we rarely get to compare different interpretations of a single role. … So last weekend, I was fascinated to see what would happen with Pina Bausch’s Kontakthof, performed by a senior cast (men and women aged over 65), and then, on the following night, by a junior cast (aged under 19).”