Starting on page 41 of Dirac's The Principles of Quantum Mechanics, he defines $f(\xi)$ in general to be that linear operator which satisfies
$$f(\xi)|\xi'\rangle = f(\xi')|\xi'\rangle\tag {34}$$
for every eigenket $|\xi'\rangle$ of the real dynamical variable $\xi$, $f(\xi')$ being a number for each eigenvalue $\xi'$
He then defines the conjugate complex $\overline{f(\xi)}$ of ${f(\xi)}$ by the conjugate imaginary equation to (34) as
$$\langle\xi'|\overline{f(\xi)} = \overline f(\xi ')\langle\xi'|$$
holding for any eigenbra $\langle\xi'|$, $\overline f(\xi')$ being the conjugate complex function to $f(\xi')$
Why doesn't he write $\overline f(\xi ')$ as $\overline {f(\xi ')}$?