Object: capture 19 black disks.
 
To start: drop one White Disk on any empty square.
Then jump orthogonally over any Black Disk to an empty square beyond, removing the Black Disk. Continue jumping until you capture any 19 of the 20 Black Disks, leaving just one.
It is impossible to capture all 20.
 
The pair of starting square, ending square is unique, as is the one remaining Black Disk. The jump-path is not unique.