Equivalent Transformations of Formulas in P2 / A.B. Ugol'nikov // Vestn. Mosk. Univ., Matem. Mekhan. 2009. № 5. P. 25-32 [Moscow Univ. Math. Bulletin. Vol. 64, No 5, 2009. P. 202-208]
A new proof of the theorem of R.C. Lyndon saying that any class of identities over a finite set of Boolean functions is finitely generated is given. The original proof relied on E.L. Post's description of all closed classes of Boolean functions. J. Berman provided another proof of this theorem which is not based on description of Post's structure, but uses some results from universal algebras.
Key words: formulas, identities, equivalent transformations.