def closest(L):
    # Base case
    if len(L) == 2:
        return L
    
    # Recursive case
    if len(L) > 2:
        closestRest = closest(L[1:])
        if (L[1] - L[0]) <= (closestRest[1] - closestRest[0]):
            return L[0:2]
        else:
            return closestRest