def add(x,y):
    """
    Returns the sum x+y
    
    This works on any types that support addition (numbers, strings, etc.)
    
    Parameter x: The first value to add
    Precondition: x supports addition and x is same type as y
    
    Parameter x: The second value to add
    Precondition: x supports addition and x is same type as y
    """
    return x+y