Cell Growth Problems

The square lattice is the set of all points of the plane whose Cartesian coordinates are integers. A cell of the square lattice is a point-set consisting of the boundary and interior points of a unit square having its vertices at lattice points. An n-omino is a union of n cells which is connected and has no finite cut set. The set of all n-ominoes, Rn is an infinite set for each n; however, we are interested in the elements of two finite sets of equivalence classes, Sn and Tn , which are defined on the elements of Rn as follows: Two elements of Rn belong to the same equivalence class (i) in Sn , or (ii) in Tn , if one can be transformed into the other by (i) a translation or (ii) by a translation, rotation, and reflection of the plane.