Sukaku

Sukaku is a logic puzzle. A number must be entered in each cell, whereby no number may appear more than once in any row, column or area.

Rules: Enter a number from 1 to 9 in each cell of the diagram so that each number occurs exactly once in each row, in each column and in each region.
Additional rules: The number in a cell must be one of the small numbers in the upper left corner of the cell.