Set difference calculator

This browser-based program performs the set difference operation of two or more sets. Set difference of sets A and B (sometimes called the relative complement of B in A) is a set C that includes all the elements of the first set A that are not included in the second set B. Usually, the difference of sets A and B is denoted as A\B, but sometimes you can find the notation A–B and A~B. Using the set-builder notation, the set difference can be defined as follows: A\B = {x: x ∈ A and x ∉ B}. Unlike the union and intersection operations, which are commutative, the relative complement isn't commutative and the order of sets is important. For example, if A = {1, 2, 3} and B = {2, 3, 4, 5}, then A\B = {1} but B\A = {4, 5}. The complement of three or more sets is calculated in a similar way. For example, {a, b, c, d, e, f} \ {a, b} \ {e, f} = {c, d}. If A ⊆ B (A is a subset of B), then A\B = ∅, and if A and B are disjoint sets (they don't have common elements) then A\B = A and B\A = B. The sets that you want to calculate the difference of must be entered in the input field and there has to be a special marker line that contains three dashes "---" between them. Optionally, you can change this marker line in the options. All input sets should be fully enumerated and written in the Roster set notation format. By default, it's a comma-delimited sequence of elements enclosed in curly braces, such as {2, 3, 4, b, c, d}. Optionally, you can change the Roster set notation format by adjusting the set bracket symbols and the set element delimiter symbol. For example, you can make your input sets look like this: <2; 3> or like this: [2 3]. The result of the difference operation is also a set that you can customize. Moreover, you can sort the elements of the output set alphabetically or numerically. Often, the sets you are working with are multisets. A multiset, compared to a simple set, preserves the multiplicity of its elements. That is, if a certain input element is repeated several times, then the multiset keeps all its copies. With the "Keep Element Copies" option active, the difference of two sets {2, 2, 3, 4} and {3, 4} is be {2, 2} and with this option disabled, the difference is {2}. Setabulous!