Languages Representable by Vertex-Labeled Graphs. - Igor Grunsky; Oleksiy Kurganskyy; Igor Potapov (MFCS, 2005)

On a Maximal NFA Without Mergible States. - Igor Grunsky; Oleksiy Kurganskyy; Igor Potapov (CSR, 2006)

On algebra of languages representable by vertex-labeled graphs. - Igor Grunsky; Igor Potapov; Elena Pryanichnikova (Theor. Comput. Sci., 2012)