This talk explores the connection between semantic equivalences for concrete sequential processes, represented by means of transition systems, and formats of transition system specifications using Plotkin's structural approach. For several equivalences in the linear time - branching time spectrum a format is given, as general as possible, such that this equivalence is a congruence for all operators specifiable in that format. And for several formats it is determined what is the coarsest congruence with respect to all operators in this format that is finer than partial or completed trace equivalence. I will start with an introduction to structural operational semantics, focusing on the meaning of negative premises.