1. Apparatus for generating displayable information that is expressive of a three dimensional solid, comprising: means for expressing the solid in a Constructive Solid Geometry representation thereof so as to be comprised of one or more primitive objects, said one or more primitive objects each being comprised of a plurality of faces; means for repetitively evaluating a sequence of one or more primitive objects to determine a correct image of a product of the primitive objects; and means, responsive to the operation of the evaluating means, for detecting a condition wherein a plurality of consecutive evaluations occur without causing a change in a tentative image of the product, the detecting means including means for counting consecutive evaluations that result in no change in the tentative image of the product and for generating a signal for causing an operation of the evaluating means to terminate when a number of consecutive evaluations occur that are sufficient to construct the correct image of the product, wherein the number is less than the square of the number of primitive objects in the product.