Let Φ , Ψ be symmetrically norming (s.n.) functions, let C Ψ ( H ) be the ideal of compact Hilbert space operators, associated with the s.n. function Ψ, p ⩾ 2 and let A , B , X ∈ B ( H ) be such that A, B are accretive and AX + XB ∈ C Ψ ( H ) . Then A ∗ + A X B + B ∗ ∈ C Ψ ( H ) as well, and | | A ∗ + A X B + B ∗ | | Ψ ⩽ | | AX + XB | | Ψ , under any of the following conditions: Ψ := Φ ( p ) ∗ and A (resp. B ∗ ) is quasinormal operator with its adjoint operator being 2-hyperaccretive and having the injective real part; if both A and B ∗ are quasinormal operators with its adjoint operators being 2-hyperaccretive operators and having injective real parts. Also, for M , N ∈ N which are such that K := ( M + N ) / 2 ∈ N , for I , J ∈ N ∪ { 0 } , for s.n. functions Φ , Ψ , for bounded Hilbert space operators A , B , X , such that A is ( M + I ) -hyperaccretive and B ∗ is ( N + J ) -hyperaccretive, satisfying Δ A , B K ( X ) = def ∑ k = 0 K ( K k ) A K − k X B k ∈ C Ψ ( H ) , then there exists V A , B M + I , N + J , − X = def lim w lim T → + ∞ ( Δ A ∗ , A M + I ( I ) ) 1 / 2 e − T A X e − T B ( Δ B , B ∗ N + J ( I ) ) 1 / 2 and | | ( ∑ m = 0 M + I ( M + I m ) A ∗ m A M + I − m ) 1 2 X ( ∑ n = 0 N + J ( N + J n ) B N + J − n B ∗ n ) 1 2 − V A , B M + I , N + J , − X | | Ψ ⩽ ( M − 1 ) ! ( N − 1 ) ! ( M + N 2 − 1 ) ! | | ( ∑ i = 0 I ( I i ) A ∗ i A I − i ) 1 2 ∑ k = 0 K ( K k ) A K − k X B k ( ∑ j = 0 J ( J j ) B J − j B ∗ j ) 1 2 | | Ψ , hold under any of the following conditions: if p ⩾ 2 , Ψ := Φ ( p ) ∗ and A or B ∗ is normal (in which case V A , B M + I , N + J , − X = 0 ), if both A and B ∗ are normal (in which case V A , B M + I , N + J , − X = 0 ), if | | ⋅ | | Ψ := | | ⋅ | | 1 and AX + XB ∈ C 1 ( H ) .
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