def is_monotonic(a,b,c):
    """
    Determines if the three input numbers are in sequence, either low-to-high
    or high-to-low (with ties acceptable).
    
    Parameters
    ----------
    a : float
    b : float
    c : float
        
    Returns
    ----------
    boolean
        
    """
    # if b is equal to either a or c then the sequence is monotonic
    if b == a:
        return True
    elif b == c:
        return True
    # otherwise, a and c must be on different sides of b
    elif (a > b) != (c > b):
        return True
    else:
        return False