  We show that any given function can be approximated with arbitrary precision
by solutions of linear, time-fractional equations of any prescribed order.
  This extends a recent result by Claudia Bucur, which was obtained for
time-fractional derivatives of order less than one, to the case of any
fractional order of differentiation.
  In addition, our result applies also to the $\psi$-Caputo-stationary case,
and it will provide one of the building blocks of a forthcoming paper in which
we will establish general approximation results by operators of any order
involving anisotropic superpositions of classical, space-fractional and
time-fractional diffusions.
