Generalized transformation semigroups having proper dense subsemigroups
Amorn Wasanawichit, Yupaporn Kemprasit, Sidney S. Mitchell · 1994
For any sets X, Y, let ? (X, Y) = the set of all mappings from X into Y, ?? (X, Y) = the set of all mappings from subsets of X into Y and ℐ (X, Y) = the set of all 1-1 mappings from subsets of X in Y. If ? (X, Y) is any one of the sets ? (X, Y), ??(X, Y)