docs: public <R> DeltaIteration<T, R> iterateDelta(DataSet<R> workset, int maxIterations, int... keyPositions) {
  		Preconditions.checkNotNull(workset);
  		Preconditions.checkNotNull(keyPositions);
  
  		Keys.ExpressionKeys<T> keys = new Keys.ExpressionKeys<>(keyPositions, getType());
  		return new DeltaIteration<>(getExecutionEnvironment(), getType(), this, workset, keys, maxIterations);
  	}