N.B. OKELO , J.O. AGURE , P.O. OLECHE . VARIOUS NOTIONS OF ORTHOGONALITY IN NORMED SPACES[J]. Acta mathematica scientia, Series B, 2013 , 33(5) : 1387 -1397 . DOI: 10.1016/S0252-9602(13)60090-9

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