Shtrakov, Sl., “Essential arity gap of Boolean functions”, Journal of Computing, Serdica, 2:3 (2008), 249–266; arXiv:0808.3892
Shtrakov, Sl., “Essential variables and positions in terms”, accepted, J. Algebra Universalis, 2008, 1–17
Shtrakov, Sl., “Multi-Solid Varieties and Mh-transducers”, Journal of Algebra and Discrete Mathematics, 2007, № 3, 113–131; arXiv:math/0702454
Denecke, K., Koppitz, J., Shtrakov, “Multi-Hypersubstitutions and Colored Solid Varieties”, International Journal of Algebra and Computation, 16:4 (2006), 797–815; arXiv:0811.4764
Koppitz, J., Shtrakov, “On mappings of terms determined by hypersubstitutions”, Journal of Algebra and Discrete Mathematics, 2005, № 3, 18–29; arXiv:0811.3325
; arXiv:0808.3892 
