Lists every single quads of four natural numbers from 0 to 9 inclusive that, once used exactly once each to add, subtract, multiply, and divide with each other, can result in 24 (as well as ones that can not).
Note that different permutations of the same four numbers are not repeated. The numbers are ordered in ascending order. For example, (2, 9, 7, 4) and (4, 2, 7, 9) are not listed —only (2, 4, 7, 9) is.
The Haskell code used to generate these quads are also given. The file generates a list of all possible expression trees produced by each quad and tests whether there is a single expression tree that evaluates to 24. If there is, the quad is considered a 'possible' one.
The generalPossibleStarts function is provided as an extra —it can be used to compute the
possible quads for any 'game' given the same rule, but with a different natural number as a goal
e.g. 32 instead of 24.
Currently, there is a QuickCheck test which generates random expression trees with four numbers and tests that the expression is covered by the rest of the code i.e. that it evaluates to the same value as a non-randomly generated expression tree. The quad files are only written if this test passes.