  The hyperfinite $G$-expectation is a nonstandard discrete analogue of
$G$-expectation (in the sense of Robinsonian nonstandard analysis). A lifting
of a continuous-time $G$-expectation operator is defined as a hyperfinite
$G$-expectation which is infinitely close, in the sense of nonstandard
topology, to the continuous-time $G$-expectation. We develop the basic theory
for hyperfinite $G$-expectations and prove an existence theorem for liftings of
(continuous-time) $G$-expectation. For the proof of the lifting theorem, we use
a new discretization theorem for the $G$-expectation (also established in this
paper, based on the work of Dolinsky et al. [Weak approximation of
$G$-expectations, Stoch. Proc. Appl. 122(2), (2012), pp.664--675]).
