  The {11-22} and {11-26} twinning modes were recently put in evidence by
Ostapovets et al. (Phil. Mag, 2017)and interpreted as {101-2}-{101-2}
double-twins formed by a simultaneous action of two twinning shears. We propose
another interpretation in which the twinning modes result from a one-step
mechanism based on the same (58deg, a+2b) prototype stretch twin. . The two
twins differ from the prototype twin by their obliquity correction. The results
are compared with the classical theory of twinning and with Westlake-Rosenbaum
model of {11-22} twinning. An unconventional twinning mode recently discovered
in a magnesium single crystal based on the same prototype twin will be the
subject of a separate publication.
