Abstract
This paper explores the connection between semantic equivalences and preorders for concrete sequential processes, represented by means of labeled transition systems, and formats of transition system specifications using Plotkin's structural approach. For several preorders in the linear time-branching time spectrum a format is given, as general as possible, such that this preorder is a precongruence for all operators specifiable in that format. The formats are derived using the modal characterizations of the corresponding preorders.