Operator inequality, Mathematics(all), Covariance–variance inequality, Operator mean, Generalizations of inner products (semi-inner products, partial inner products, etc.), operator mean, Norms (inequalities, more than one norm, etc.) of linear operators, Semi-inner product C∗-module, operator inequality, General theory of \(C^*\)-algebras, Kantorovich inequality, \(C^*\)-modules, covariance, semi-inner product \(C^{\ast }\)-module, C∗-algebra, Inequalities for sums, series and integrals, \(C^{\ast }\)-algebra, Linear operator inequalities, variance inequality