  It was recently demonstrated that N=1,2,3,4 super-Schwarzian derivatives can
be constructed by applying the method of nonlinear realisations to
finite-dimensional superconformal groups OSp(1|2), SU(1,1|1), OSp(3|2),
SU(1,1|2), respectively, thus avoiding the use of superconformal field theory
techniques. In this work, a similar construction is applied to the exceptional
supergroup D(2,1;a), which describes the most general N=4 supersymmetric
extension of SL(2,R), with the aim to study possible candidates for a D(2,1;a)
super-Schwarzian derivative.
