Proof by David Auburn

From Greenhouse Cabaret:

Proof is the story of an enigmatic young woman, Catherine, her manipulative sister, their brilliant father, and an unexpected suitor. They are all pieces of the puzzle in the search for the truth behind a mysterious mathematical proof.

In Proof, the young but guarded Catherine grieves over the loss of her father, a famous mathematician who had become a legend at the local university for solving complicated proofs, and for suffering from dementia. Just as Catherine begins to give in to her fear that she, too, might suffer from her father’s condition, Catherine’s older sister Claire returns home to help “settle” family affairs and Hal, one of the father’s old students, starts to poke around the house. What Hal discovers in an old speckle-bound notebook brings to light a buried family secret.

It tests the sisters’ kinship as well as the romantic feelings growing between Catherine and Hal.

This poignant drama about love and reconciliation unfolds on the back porch of a house settled in a suburban university town, that is, like David Auburn’s writing, both simple and elegant.