Jewels and Duality (Entrance)
The brief
Welcome to the entrance of an underground jewel mine. Normal 4x4 sudoku rules apply.
Grey lines are INDEX LINES. The digit in position N along an index line (starting from the end with diamond) indicates the position along the line where the digit N should be placed. Eg: An index line could read 3214; the 1st digit being a 3 indicates that the 3rd digit is a 1, and so on.