“…Actually, it was Naȋmark [605,606,607] who investigated different types of extensions (with exit) and a proper interpretation then yields the corresponding resolvent formula. For the notion of Štraus family and for Kreȋn's formula for exit space extensions we refer to [491,492,679] and to [726,727,728,729,730,731,732,733]; some other related papers are [51,121,126,219,234,237,254,266,320,497,523,554,595,596,624]. The Štraus families are restrictions of the adjoint in terms of "λ-dependent boundary conditions" given by a Nevanlinna family or corresponding Nevanlinna pair.…”