High-z Sudoku: A diagnostic tool for identifying robust (sub)mm
  redshifts
  We present methods to (i) graphically identify robust redshifts using
emission lines in the (sub)mm regime, (ii) evaluate the capabilities of
different (sub)mm practices for measuring spectroscopic redshifts, and (iii)
optimise future (sub)mm observations towards increasing the fraction of robust
redshifts. Using this publicly-available code
(https://github.com/tjlcbakx/redshift-search-graphs), we discuss scenarios
where robust redshifts can be identified using both single- and multiple-line
detections, as well as scenarios where the redshift remains ambiguous, even
after the detection of multiple lines. Using the redshift distribution of
(sub)mm samples, we quantify the efficiencies of various practices for
measuring spectroscopic redshifts, including interferometers, as well as
existing and future instruments specifically designed for redshift searches.
Finally, we provide a method to optimise the observation strategy for future
(sub)mm spectroscopic redshift searches with the Atacama Large
Millimetre/submillimetre Array, where 2 mm proves indispensable for robust
redshifts in the z = 2 - 4 region.
