Let x be given.
rewrite the current goal using HLo_def (from right to left).
An exact proof term for the current goal is HxLo.
We prove the intermediate
claim HxR:
x ∈ R.
rewrite the current goal using HHi_def (from right to left).
An exact proof term for the current goal is HxHi.
An
exact proof term for the current goal is
(RleI one_third x H13R HxR Hnlt_x_13).
Apply FalseE to the current goal.