By Jackie Demaline
The Cincinnati Enquirer

When you open your program for Proof at Playhouse in the Park, you'll notice an insert that notes Michelle Six is a replacement in the play's central role of Catherine.

I caught her second performance after she was dropped into the role (not unlike a paratrooper) over the weekend after actress Jessica Lancaster became ill. Under other circumstances this review would have been a preview, and I expect director Michael Haney will be fine-tuning through the week.

Proof is a Pulitzer Prize-winning crowd-pleaser that explores an adult daughter's relationship with her father - and the madness she fears she has inherited from him. It pushes sibling buttons. It even has a charming love story. It is about trust on many levels and manages to be smart and funny. The sentimental ending is the proverbial cherry on top.

If that weren't enough to ring those box office bells, playwright David Auburn schmoozes the audience into believing we could understand the high mathematics of a math proof. Talk about a feel-good show.

One of Proof's pleasures is that Mr. Auburn has written many surprises into his script. (If you already know them, the play isn't as much fun on second viewing.)

Ms. Six, for all her actressy delivery, does some good work. But in this early performance she cut the bottom out of the show because its central mystery is about Catherine and her underlying fear that she has inherited her father's madness.

Her Catherine is saner than sane, so when her disagreeable elder sister (Rachel Fowler) keeps implying that Cath needs a little rest cure, she comes off as evil or crazy. It doesn't help that the single chord Ms. Fowler plays is "uptight," which becomes a sort of drone.

The performance worth watching is Playhouse regular Robert Elliott as Catherine's dad. Proof moves around in time, so Mr. Elliott lets us meet him in charming sanity and belligerent madness and even in disintegration. Ms. Six's strongest moments are shared with him. Their second-act scene is a wow.

New in Catherine's life is Hal, math geek, one-time protÈgÈ of Catherine's father and good guy (if a little disappointing in the trust department). He's delightfully played by Christopher Kelly.

The drama plays out on the back porch of a big, old, ill-kept house (by the looks of the well-worn wicker furniture and rusting grill and torn striped awning) that you know is within walking distance of a university. It's a nice sense of place by set designer Paul Shortt, although autumn seems to have come awfully early.

Proof, through Feb. 14, Playhouse in the Park Marx Theatre, 421-3888.

E-mail jdemaline@enquirer.com.