def findInteraction(interactions, roadUserNum1, roadUserNum2):
    """Returns the right interaction in the set"""
    i = 0
    while i < len(interactions) and set([roadUserNum1, roadUserNum2]
        ) != interactions[i].getRoadUserNumbers():
        i += 1
    if i < len(interactions):
        return interactions[i]
    else:
        return None
