1. A computer program product having a computer readable medium having computer program logic recorded thereon for determining interactions between to isothetic rectangles each of said rectangles having four vertices including upper left, upper right, lower left and lower right, said computer program product comprising: means for determining a first combined relative displacement based upon at most two vertices of said rectangles; means for determining a relationship between the rectangles if said first combined relative displacement is determinitive; means for determining a second combined relative relationship based upon at most two vertices of said rectangles, said at most two vertices being different than the previously tested two vertices; and means for determining the relationship of the rectangles based on the first and second combined relative displacements.