Divide and congruence II: From decomposition of modal formulas to preservation of delay and weak bisimilarity

Earlier we presented a method to decompose modal formulas for processes with the internal action τ, and congruence formats for branching and η-bisimilarity were derived on the basis of this decomposition method. The idea is that a congruence format for a semantics must ensure that the formulas in the modal characterisation of this semantics are always decomposed into formulas that are again in this modal characterisation. In this follow-up paper the decomposition method is enhanced to deal with modal characterisations that contain a modality 〈ϵ〉〈a〉φ, to derive congruence formats for delay and weak bisimilarity.