D                       This is an internal function. It calculates the
                        criterion function for semiparametric
                        estimation.
K_Y                     This is an internal function. The
                        anti-derivative of the kernel function.
NRDD                    Nonlinear RDD estimator
g                       This is an internal function. The structural
                        function.
h0                      This is an internal function. The treatment
                        choice function below the cutoff, used for the
                        data generating function nrddgp.
h1                      This is an internal function. The treatment
                        choice function above the cutoff, used for the
                        data generating function nrddgp.
k                       This is an internal function. The kernel
                        function
nrdbw                   Bandwidth selector for nonlinear RDD
nrddgp                  Data generating process for nonlinear RDD
nrdse                   Standard error for nonlinear RDD
