Normal sudoku rules apply. In this puzzle, each digit from 1-9 is represented by a letter from A-I. You must determine which letter represents which digit. When discovered, these can be entered into the orange boxes at the bottom. The 2x2 area surrounding a quad circle must contain all the digits represented by the letters in that circle. The digits along a grey line can be divided into one or more non-overlapping groups of adjacent cells, each of which sums to 10. The digits in a blue or yellow cage must sum to the total in the top left corner. Enter correct digits near the grey fog cells to clear the fog. No guessing is necessary.