An air of mystery imbues three notably distinct works, grounded by Balanchine’s masterful homage to Russian classicism. The evening’s mysticism is well-established by La Sonnambula, the tantalizing tale of an ill-fated romance between a poet and the titular apparition. The choreographer’s unflinching commitment to innovation and musicality is on full display in the centerpiece ballets, both of which feature shocking pas de deux inspired by their challenging scores: 1968’s Pithoprakta, set to Iannis Xenakis’s stochastic composition of the same name, revived following a lengthy hiatus from the company stage; and The Unanswered Question from 1958, with music by American composer Charles Ives. Theme and Variations responds to these provocations with a tribute to classical choreography, made new in Balanchine’s dazzling approach, incorporating original, complex movement and his distinct musicality.