Photo: In Her Father''s Shadow: Lucinda Serrano (above) is at the heart of an academic storm; Serrano battles Tim Hart for the rights to a proof.

The winner of both a Tony Award and a Pulitzer Prize in 2001, David Auburn''s Proof is a richly compelling drama, as philosophical as it is personal. The current production by Pacific Repertory Theater leaves a lasting impression.

The story revolves around Catherine, who has just turned 25 as the play opens. The daughter of a once-famous mathematician, Catherine has inherited both his talent for math and his tendency toward madness. When her father, Robert, went nuts eight years prior to the play''s beginning, Catherine quit school to care for him, while big sister Claire went to work and paid the bills.

Coinciding with Catherine''s birthday is her father''s funeral, for which Claire has returned home. During the funeral reception, Catherine embarks on a romantic relationship with Hal, one of Robert''s former students, who has been going through the latter''s notebooks trying to find something of value buried among the lunatic ravings.

When Catherine produces a notebook containing a revolutionary proof concerning prime numbers--and claims to have written it herself--Claire and Hal are presented with a host of questions: Is Catherine lying? Is she a genius? Or is she as mad as her father? And, most importantly, how is any of this proven?

On the one hand, the play is about the relationships between the four characters. At the same time, it''s a Kierkegaardian exploration into the moments of anxiety and doubt that precede any true leap of faith. And, like Kierkegaard, Auburn seems to come to the same conclusion: In the end, proof is less attainable or valuable than faith.

Director John Rousseau delivers an excellent, thoughtful production. His ensemble cast--Michael Jacobs as Robert, Lucinda Serrano as Catherine, Julie Retzlaff as Claire, and Tim Hart as Hal--works together seamlessly, crafting believable relationships and sympathetic characters. Doubling as scenic designer, Rousseau moves his actors around the warmly toned and textured backyard of an aging Chicago home. As his actors fan out from the backdoor of the house, they always seem drawn back to the mystery contained indoors.

As the troubled Catherine, Lucinda Serrano gives a finely detailed performance. Serrano not only shows us a deeply depressed young woman who simultaneously loves and resents her father and sister but she also shows us small sparks of life that give us hope for the character. Michael Jacobs, too, offers a very engaging character. Appearing mostly as a ghost to daughter Catherine, offering fatherly advice and encouragement, Jacobs exudes warmth and compassion. In the flashback scenes to when Robert was alive, we see why he was a favorite among his students. And, when the cracks begin to recur in his unhinged mind, Jacobs handles the task with delicacy, creating an obviously thin veneer of sanity through which the madness is beginning to seep.

As Claire, Julie Retzlaff has the difficult task of portraying a character that is both overbearing and genuinely compassionate, and she does a beautiful job. As the character is written, Claire could be unlikable, but Retzlaff offers a slightly bubbly, slightly vulnerable woman. Yes, she''s selling her father''s home and forcing Catherine to move to New York with her, but she''s doing it because she cares about her sister, and, particularly in her final scene, Retzlaff reveals not only her character''s frustration but also her compassion.

Rounding out the cast is Tim Hart as a delightfully geeky Hal. Hart''s nasal voice and disheveled hair create the typical nerd, but here, too, the performance goes deeper than cardboard-cutout stereotype. Hart gives a human depth to his predicament as his character is forced to make several leaps--the awkward first kiss, the delivery of a doctoral dissertation to a famous man, the decision about whether to believe Catherine''s claims to authoring the revolutionary proof.

All told, this is an excellent production, enhanced by the intimacy of the Circle Theater. Audiences are encouraged to take a leap of faith and go see for themselves.

Proof continues at the Circle Theater through 3/30. 622-0100.