Pennsylvania Playhouse has delivered an enjoyably intimate and gripping production of the Pulitzer Prize winning play "Proof."

The haunting and satisfying show is at Pennsylvania Playhouse, 390 Illicks Mill Road, Bethlehem through Feb. 11.

"Proof" tells the story of Catherine, the daughter of a recently deceased mathematical genius, and her struggle with mathematical genius and mental illness.

On the eve of her twenty-fifth birthday, Catherines father, Robert, a math professor at the University of Chicago, has recently died, after a struggle with mental illness, and Catherine must deal with her Type A sister and Hal, her fathers ambitious former graduate student who hopes to find valuable work in the 103 notebooks that Robert left behind, as well as deal with her own long denied feelings and fears.Proof6

Its a haunting play that blends together many elements with a touch of humor. The title refers to both the mathematical proofs that Robert published in his younger years and to how Catherines own mathematical genius is doubted in the male-dominated field.

As the troubled Catherine, Gabrielle Hondorp gives a thoughtful and nuanced performance. Hondorps Catherine is brittle, but with a palpable anger and frustration bubbling just below the surface. Hondorp brings to life Catherines mixed emotions that result from her having given up her own studies five years earlier to become her fathers full-time caregiver.

As Catherines pushy sister Claire, Brooke Harrsch is cloyingly perfect as first but soon reveals the characters underlying resentment and unresolved guilt. Harrschs Claire is that over-compensating sister whose single-minded self-assurance is at first funny until it turns threatening.

Andrew Maldonados Hal is likable, although at times his motives are in question. Maldonaldo gives Hal a sincerity and vulnerability, as well as an amusing awkwardness. Maldonado makes Hals burgeoning romance with Catherine sweet and spontaneous and Maldonaldo and Hondorp have a gentle chemistry.

Dale Beltzners Robert is engaging and charmingly paternal with Catherine. Beltzner also is believable as a true genious excited by discovery, as well as a man trying desperately to hold onto his sanity.

Director Mark Stutz handles the plots several twists and turns with aplomb and brings out the gentle humor of the play. He elicits strong performance from his four talented leads as they navigate situations which change quickly. The pacing is fast and the show moves swiftly through its two hours and 20 minutes, with intermission.

Designer Brett Oliveira has created a cozy set in which the boards of the outdoor decking morph into a pattern of mathematical equations cleverly showing the intersection of the characters internal and external lives. Oliveiras evocative lighting enhances the mood.

The cast and staff will be hold audience talk backs after the shows Jan. 27, Feb. 3 and 10.

Tickets are $25, adults; $22, seniors and $15 students.The Feb. 3 performance will be "Pay What You Are Able."

Performances are 7:30 p.m. Jan. 26, 27, Feb. 2, 3, 9, 10; and 3 p.m. Jan. 28, Feb. 4, 11. For information, call 610-865-6665.