Upper panel: P vs. K − [22] diagram with linear least-squares fits to different sub-samples of Miras. Blue dashed line: Fit to the Tc-poor Miras (filled blue circles), excluding the identified outliers (open circles, see text). Red dashed line: Same for the Tc-rich Miras (filled and open red circles, respectively). Black solid line: Fit to all Miras. Lower panel: P vs. K − [22] diagram with the linear relation that best separates Tc-poor from Tc-rich Miras (Eq. 1).