Cages and sums
Normal sudoku rules apply: 1–9 once in every row, column and box. Dashed cages add a rule: their digits must add up to the small total. A digit can never repeat within a cage, even when it crosses a box boundary.
Worked example
A two-cell cage with total 4 must contain 1 and 3. The alternative 2 + 2 is ruled out because a digit cannot repeat within a cage. Use rows, columns and boxes to determine their order.