  Binary delta-matroids are closed under vertex flips, which consist of the
natural operations of twist and loop complementation. In this note we provide
an extension of this result from GF(2) to GF(4). As a consequence, quaternary
matroids are "safe" under vertex flips (vf-safe for short). As an application,
we find that the matroid of a bicycle space of a quaternary matroid is
independent of the chosen representation. This extends a result of Vertigan [J.
Comb. Theory B (1998)] concerning the bicycle dimension of quaternary matroids.
