Structured Programs for Turing Machines. - Solomon Passy (Inf. Process. Lett., 1980)

Quantifiers in combinatory PDL: completeness, definability, incompleteness. - Solomon Passy; Tinko Tinchev (FCT, 1985)

PDL with Data Constants. - Solomon Passy; Tinko Tinchev (Inf. Process. Lett., 1985)

Determinism and Looping in Combinatory PDL. - George Gargov; Solomon Passy (Theor. Comput. Sci., 1988)

Using the Universal Modality: Gains and Questions. - Valentin Goranko; Solomon Passy (J. Log. Comput., 1992)