Performs 'nonlinear Invariant Causal Prediction' to estimate the
causal parents of a given target variable from data collected in
different experimental or environmental conditions, extending
'Invariant Causal Prediction' from Peters, Buehlmann and Meinshausen (2016),
, to nonlinear settings. For more details, see C. Heinze-Deml,
J. Peters and N. Meinshausen: 'Invariant Causal Prediction for Nonlinear Models',
.