Full Idea
With system B we begin to be able to say something about iterated modalities. ..S4 then takes a different stand on the iterated modalities, and neither is an extension of the other.
Gist of Idea
System B introduces iterated modalities
Source
Theodore Sider (Logic for Philosophy [2010], 6.4.4)
Book Reference
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.168
Related Idea
Idea 13704 It is hard to say which are the logical truths in modal logic, especially for iterated modal operators [Sider]