Abstract: We introduce a new family of binary composition operators that solves four major problems of constructive implicit modeling: suppressing bulges when two shapes merge, avoiding unwanted blending at a distance, ensuring that the resulting shape keeps the topology of the union, and enabling sharp details to be added without being blown up. The key idea is that field functions should not only be combined based on their values, but also on their gradients. We implement this idea through a family of $C^∞$ composition operators evaluated on the GPU for efficiency, and illustrate it by applications to constructive modeling and animation.