def ar_and(x, y, nx, ny):
    """Dimensionless production rate for a gene regulated by one
    activator and one repressor with AND logic in the absence of
    leakage.

    Parameters
    ----------
    x : float or NumPy array
        Concentration of activator.
    y : float or NumPy array
        Concentration of repressor.
    nx : float
        Hill coefficient for activator.
    ny : float
        Hill coefficient for repressor.

    Returns
    -------
    output : NumPy array or float
        x**nx / (1 + x**nx + y**ny)
    """
    return x ** nx / (1 + x ** nx + y ** ny)
