Andirkonis, J. (2009) “Loop-free sequent calculus for modal logic K4”, Lietuvos matematikos rinkinys, 50(proc. LMS), pp. 241–246. doi:10.15388/LMR.2009.43.
In the article, a loop-free calculus for modal logic K4 is presented. The calculus is based on marks and indices method which was first used for logic S4.