“…We refer to works by Korolyuk et al (1974), Kovalenko (1975), Turbin (1976, 1978), Courtois (1977), Silvestrov (1980b), Anisimov et al (1987), Ciardo et al (1990), Kovalenko et al (1997), and Korolyuk and Korolyuk (1999), Limni-os andOprişan (2001, 2003), Barbu et al (2004), Zhang (2005, 2013), Manca (2006, 2007), Anisimov (2008), Gyllenberg and Silvestrov (2008), , and Papadopoulou (2013).…”