```erlang 1.sofs:range(). inout->sofs:relation([{1,2},{1,3},{2,4},{2,5}]) outout ->{'Set',[2,3],atom} 2.sofs:relation(). input ->[{1,2},{1,3},{2,4},{2,5}] output ->{'Set', [{1,2},{1,3},{2,4},{2,5}],{atom,atiom}} 3.sofs:to_external(). input ->{'Set', [2,3],atom} output -> [2,3] ```