  This paper investigates quasi-selfadjoint extensions of dual pairs of linear
relations in Hilbert spaces. Some properties of dual pairs of linear relations
are given and an Hermitian linear relation associated with a dual pair of
linear relations is introduced. Necessary and sufficient conditions for
quasi-selfadjoint extensions of dual pairs of linear relations are obtained.
These results extends the corresponding results for dual pairs of linear
operators to dual pairs of linear relations.
