def find_dependent_helpers(helpers,dependency):
	"""
	Returns a list of helpers depending on `dependency` and their respective derivative (applying the chain rule).
	"""
	
	dependent_helpers = []
	
	for helper in helpers:
		derivative = sum(
				(
					helper[1].diff(other_helper[0]) * other_helper[1]
					for other_helper in dependent_helpers
				),
				helper[1].diff(dependency)
			)
		if derivative != 0:
			dependent_helpers.append( (helper[0], derivative) )
	
	return dependent_helpers