“…Theorem 3.1. (Kozachenko et al (2011)) Suppose that { ( ), ∈ } is a centered second-order random process with the correlation function ( , ) = E ( ) ( ), ( , ℬ , ) is a measure space, { ( ), ∈ ℤ} is an orthonormal basis in 2 ( , ) and ( ,⋅) ∈ 2 ( , ), ∈ .…”