Daowu Pei Guojun Wang The extensions L<sub>n</sub><sup>*</sup> of the formal system L<sup>*</sup>and their completeness. 155-166 2003 152 Inf. Sci. http://dx.doi.org/10.1016/S0020-0255(02)00406-1 db/journals/isci/isci152.html#PeiW03