Created code for converting lists to tuples for the parameters of buildTree.
Removed redundant where clause in solveTree.
Added support to show the symbols of the operators when printed.
Made solutionsFromNumCombs more elegant by using map.
Updated the parameter order of solutionsFromOpCombs to work with the partial application in solutionsFromNumCombs. Also using concat to flatten the list of solutions in solutionsFromNumCombs.