Operator brackets, also known as Bra-kets (angle brackets with a vertical line in between), are common in Physics notation: &quot; langle a mline b rangle &quot; or &quot; langle a mline b mline c over d mline e rangle. &quot; The height and positioning of the vertical lines always corresponds exactly to the enclosing brackets.
尖括号之间加上一条垂直线的用法在物理学中相当普遍： &quot; langle a mline b rangle &quot; 或 &quot; langle a mline b mline c over d mline e rangle &quot; 。垂直线的高度和位置总是与括号相一致。