Proof, Menier Chocolate Factory, London

©Nobby Clark

Family functions: Mariah Gale and Matthew Marsh

Mathematicians, according to young academic Hal, like rock stars and footballers, have a “Best Before” date. “It’s a young man’s game,” Hal explains (poignantly, at 28, he’s already over the hill) to the daughter of his deceased tutor. Those past their prime (pardon the pun), he adds, may seek a little chemical help balancing the equation.

His assertion matters here because age may play a part in a crucial argument about proof. When Hal finds a groundbreaking solution to a theorem among the old man’s jottings, the question as to who wrote it becomes the driving force of David Auburn’s play.

Proof, first staged in 2000, never budges from a Chicago townhouse, home to the mathematical genius Robert and his 25-year-old daughter, Catherine. But it handles vast themes. Catherine, we learn, dropped out of university to care for her father, whose early mathematical virtuosity dwindled into mental illness and decline. His death brings two visitors: Hal, keen to sift through Robert’s papers in case he did write something of value in his last years; and Claire, Catherine’s sister, who is eager to rescue Catherine from this depressing environment. When Hal finally discovers a notebook containing a thrilling new mathematical proof, things turn critical. Who wrote it? Could Catherine have inherited her father’s gift? And, if so, what else did she inherit?

The play turns on the several meanings of the word proof – mathematical, evidence-based and resistant to damage – and the role that trust has to play amid the hunt for solutions. It’s witty and a gripping watch, though not quite as deep or dazzling as you might hope. It doesn’t have the scope and brilliance of Arcadia, neither does it match form and content so excitingly as Constellations, Copenhagen or A Disappearing Number. And even for non-mathematicians, the play’s vagueness about the detail of the discovery is frustrating and leaves a hole at the centre of the drama.

It is beautifully acted, though, in Polly Findlay’s taut new production. Jamie Parker’s Hal deftly combines decency and craftiness, as he grapples with the pluses and minuses of his awkward situation. Emma Cunniffe brings lovely timing to the well-meaning but overbearing sister, while Matthew Marsh, as the dead-but-still-present father gives a touching portrayal of a great bear of a man, sadly diminished. And Mariah Gale is riveting as Catherine: pale, awkward, tough yet fragile, she suggests the rare thrill of intellectual adventure and the terror of mental infirmity.

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