 The phrase “logical frameworks” has been used in ways other than that introduced in Section  2,  e.g., in Huet and Plotkin (1991). The use of “≻” here as a sequent separator is occasioned by current HTML font limitations; its general use for that purpose is not recommended. Carnap’s observation about logic pursued in  Set-Fmla not being capable of enforcing the intended truth-functional interpretation of various connectives (such as ∨, ¬, and →) has received extensive attention in the literature, as was mentioned in the first paragraph of this section. The term “congruential” used here is taken from Segerberg (1982); it is based on a related use of the term by D. Makinson (for modal logics in Fmla containing ☐ φ ↔ ☐ ψ whenever they contain φ ↔ ψ). In some quarters the term “self-extensional” is used for congruentiality, while in others the term “extensional”—used quite differently here—is used for this property.