My father is an artist who is considering building a sculpture for an organization. as part of the contract he is prohibited from making copies of the sculpture in the future, or any works that are not "materially different".
Nothing in this Agreement shall, however, prevent the Artist from making other works of art that are materially different than the Artwork using combinations of the same materials and in different configuration".
What does "materially different" mean in this case? How different do future sculptures need to be to qualify?