  The three kinds of parameter degeneracy in neutrino oscillation, the
intrinsic, sign and octant degeneracy, form an eight-fold degeneracy. The
nature of this eight-fold degeneracy can be visualized on the
($\sin^22\theta_{13}$, $1/\sin^2\theta_{23}$)-plane, through quadratic curves
defined by $P(\nu_\mu\to\nu_e)=$ const. and $P(\bar{\nu}_\mu\to\bar{\nu}_e)=$
const., along with a straight line $P(\nu_\mu\to\nu_\mu)=$ const. After
$\theta_{13}$ was determined by reactor neutrino experiments, the intrinsic
degeneracy in $\theta_{13}$ transforms into an alternative octant degeneracy in
$\theta_{23}$, which can potentially be resolved by incorporating the value of
$P(\nu_\mu\to\nu_\mu)$. In this paper, we analytically discuss whether this
octant parameter degeneracy is resolved or persists in the future long baseline
accelerator neutrino experiments, such as T2HK, DUNE, T2HKK and ESS$\nu$SB. It
is found that the energy spectra near the first oscillation maximum are
effective in resolving the octant degeneracy, whereas those near the second
oscillation maximum are not.
