On self-adjoint operators in Krein spaces constructed by Clifford algebra Cl2

Let J and R be anti-commuting fundamental symmetries in a Hilbert space ℘. The operators J and R can be interpreted as basis (generating) elements of the complex Clifford algebra Cl2(J,R) := span{I, J;R, iJR}. An arbitrary non-trivial fundamental symmetry from Cl2(J,R) is determined by the formula [formula]. Let S be a symmetric operator that commutes with Cl2(J,R). The purpose of this paper is to study the sets [formula] of self-adjoint extensions of S in Krein spaces generated by fundamental symmetries [formula]. We show that the sets [formula] and [formula] are unitarily equivalent for different [formula] and describe in detail the structure of operators [formula] with empty resolvent set.