Four hands = 20 digits x two pianos x 88 keys. That seems a sensible formula for the musical possibilities of a piano duet presentation.

But if you're adding South African geniuses Kathleen Tagg and Andre Peterson to the equation, forget any "rules" or "finite realities" and just let them intuitively interact and extrapolate and, to put it in terms Bach or Cedar Walton might've used, "sorta go harmonically nuts."

Tagg and Peterson, whose solo careers have been groundbreaking and visionary across the fields of jazz (Peterson), contemporary classical (Tagg), South African and improvisational, teamed in 2017 for the stunning and accurately named "When Worlds Collide" album. Now the duo is touring and performs Friday at Connecticut College.

This concert, part of Conn's esteemed Guest Artist Series, should kick a hole in whatever your perception of "piano playing" might be, and the results will be as melodically pleasing as they are structurally amazing.

When Worlds Collide — Kathleen Tagg and Andre Peterson, 7:30 p.m. Friday, Evans Hall, Connecticut College, 270 Mohegan Ave., New London; $22, $20 seniors, $7 student with ID; (860) 439-2787, conncoll.edu.