  The class of all t-norms is very large, and up to now not really well understood. Even for those t-norms which have the sup-preservation property the structural understanding is far from complete, but much better as for the general case: a discussion of the recent state of the art is given by Jenei (2004). Sufficiently well understood is only the further subclass of continuous t-norms: they are nicely composed out of isomorphic copies of the Łukasiewicz t-norm, the product t-norm, and the Gödel t-norm, i.e. the min-operation, as explained e.g. in Gottwald (2001).