“…In [3], we can see that A ⊥ s, # ⃝ B implies (A + B) # ⃝ = A # ⃝ + B # ⃝ (core additivity). In [4], Liu, Wang, and Wang proved that A, B ∈ C n×n with Ind(A) ≤ 1 and Ind(B) ≤ 1 are strongly core orthogonal, if and only if (A + B) # ⃝ = A # ⃝ + B # ⃝ and A # ⃝ B = 0 (or BA # ⃝ = 0), instead of A ⊥ # ⃝ B, which is more concise than Theorem 7.3 in [3]. And, Ferreyra and Malik in [3], have proven that if A is strongly core orthogonal to B, then rk(A + B) =rk(A)+rk(B) and (A + B) # ⃝ = A # ⃝ + B # ⃝ .…”