Solution to a Problem of Goranko and Passy
Frank Wolter · Journal of Logic and Computation · 1994
Goranko and Passy have defined for a monomodal logic ∧ ⊆£(□) its minimal extension ∧u ⊆ £u. ∧u is the smallest bimodal logic such that one monomodal fragment is ∧, the other is S5 and u⃞p → □p ∊ Λu. They state the problem whether for any finitely complete logic ∧ its minimal extension ∧u is finitely complete. In this paper we give a negative answer to this question.