Normal Sudoku rules apply.
Leapfrog: if a cell is next to (in any direction) a lilypad digit "N", continuing in that direction, any cell N away must also differ by N. Not all lilypads are given.
For example: if R2C1 is 3, if R3C1 (lilypad) is a 2, R4C1 can be either a 1 or a 5.