• Specification

• Source code

• Solution

1. Two useful implementations of SET are
   • http://docs.eiffel.com/static/libraries/base/two_way_sorted_set_chart.html
   • http://docs.eiffel.com/static/libraries/base/binary_search_tree_set_chart.html

Both are generic classes and require the argument to implement interface COMPARABLE (which is true about STRING and INTEGER in Eiffel. In addition they offer you search capabilities that may be useful.

1. Returning VOID from feature