The mathematics of Reich's music is aptly served by how the young dancers cluster off—like a kind of human haiku at times—in formations of five, or seven; or just to perversely disrupt the form and the formality, dissolving into twos and threes at once. There is, as with so much of de Keersmaeker's work, a geometric swing. Arms and legs point out stiff as clock hands, as the troupe of ten tilt and nearly collapse, only to spring back renewed. The energy and percision of the ever moving company is almost superhuman, exhaustive. When not running in circles, colliding or leaping, they walk hypnotically back and forth. Occasionally, they seem to emulate a kind of collective freedom, the restless undiluted energy of children, and their space, the stage, is as liberating as a junior school playground. Movements spread like gossip: where one leads, others follow. They are coquettish, goading, provoking each other.

This liminal space, complemented by the curtain of Jan Versweyveld's suspended ropes, is a simple backdrop which could represent borders; barriers or a forest. It contains the dancers, creating a new uncertain terrain, yet they can disappear and reappear at will from behind them. They are their own fortress. Peek-a-boo is played, from when Reich's ticklish instruments fall out and in the thrum. A conspiratorial trio of women leap, land and unfold as the xylophones kick in. Sometimes, they're Puckish, not unlike the Woodstock generation—although that would be anathema to Reich, who made his own minimalist soundscapes rejecting sixties cliches, and de Keersmaeker herself balks at the notion of being pigeonholed. Yet, this all melts away when some more modern movements are incorporated—a little floor spinning or somersaulting to wrongfoot the elegant sweeping motions.

Clockwork Coppélias, all surrounding a bounding balletic José Paulo dos Santos solo, they now melt into each other, and are a kaleidoscopic tangle. In their pared-down greys and creams with splashes of pink, their catch and release looks like another game. Heads are rubbed onto other's bellies, as a reassuring gesture of nurturing and solidarity.

As with the imperceptible, complex variances within the music, you cannot always notice the differences in the choreography until you sit with it for a while, then 'ah,' it registers—a look, a gesture, a bend, change of mood lighting or costume. It's cunning, teasing, so subtle. Chairs are sneaked onto the floor, some dancers peel off then sneak back in. But the mood has become melancholic, bathed in green lights.

It all culminates in a catwalk of sorts, as the dancers sashay back and forth to the front of the stage, before a defiant stare back at the audience. Laura Bachman in particular gives good sass, jutting out her hips, and with a smirk full of attitude. Others prove harder to read. But it's all playful in its abstraction. There is even a false ending. The performance, eerily, brings a light drizzle to the night air as we file out of the auditorium. Long may Rosas 'reign', as mischievous, enigmatic and hard to second guess as ever.