BURRTOOLS is capable of handling piece ranges instead of a fixed number of pieces. This feature is useful when you want to search for puzzles instead of solving a given one. If there is a range defined for one or more pieces then BURRTOOLS finds all ways to assemble the defined result using a number of pieces within the given range. As an example let's take Ronald Kint-Bruynseels Clarissa-Burr (see http://www.asahi-net.or.jp/~rh5k-isn/Puzzle/ClarissaBurr). This puzzle consists of 2 different shapes. When Ronald defined this puzzle he had to try all possible combinations of the 2 pieces, beginning with 6 pieces of shape A and zero of shape B, over 5 times A and one B up to 6 times B. This can now be done way more easily with piece ranges. Simply tell BURRTOOLS that the result should be made out of 0-6 pieces of shape A and 0-6 pieces of shape B, or if you want to ensure that at least one of each shape is used, use ranges 1-6. Then solve.
Piece ranges can be easily defined using the min=0 button. This will set the minimum of the piece range for the current shape to zero. With that you can define the range by first adding max-min pieces (meaning the difference between the maximum and the minimum number of pieces), then set the minimum to zero and then add the missing minimum pieces. This should cover the most used usage cases.
For example: suppose you want to add a piece that you want to use 3, 4, 5 or 6 times in your puzzle. The piece range is 3-6. To enter those values you first add 6-3=3 pieces. Then you press the min=0 button getting a piece range 0-3. Now you add another 3 pieces and you get the range you want.
Except for the min=0 button, all other buttons always change the minimum and the maximum of the piece range.
If this calculation is too hard for you, you can use the problem detail dialogue (see section ProblemDeatils) to enter the ranges directly without the need for calculations.