private void AddStepPattern(QilNode nd, QilNode input) {
OptimizerPatterns patt = OptimizerPatterns.Write(nd);
patt.AddPattern(OptimizerPatternName.Step);
patt.AddArgument(OptimizerPatternArgument.StepNode, nd);
patt.AddArgument(OptimizerPatternArgument.StepInput, input);
}