This method returns a constraint that states that whenever both interval variables a and b are present, the distance start(b)-start(a) between the start of interval a and the start of interval b must be greater than or equal to 0. You must add this constraint to a model and extract the model for an algorithm in order for it to be taken into account.

public IConstraint StartBeforeStart(
	IIntervalVar a,
	IIntervalVar b
)