def findLinkLabel(label, links):
	"""Checks if given label exists in list of link labels.
	
	**Arguments**
	
	*label*
	  the label to search for
	  
	*links*
	  list with link labels collected so far, 
	  list contains tuples of (label, filename, line nr., description, is_duplicate)

	**Returns**
	
	Tuple with existing link label information or None if it does not yet exist in list.
	"""
	
	for l in links:
		if l[0] == label:
			return l
	return None