def α_L(α_G): # (5)
    """
       Calculates liquid phase volume fraction at the next spatial step. Hence,
       the argument it takes assumes its value at the next spatial step also.

       Args:
           α_G (float) - gaseous phase volume fraction. Can assume any value
                         from 0 to 1.

       Returns:
           float: the return value (liquid phase volume fraction). Can assume
                  any value in the range 0 to 1.

       Example:
           α_L(0.3) = 0.7 - both entities are dimensionless
    """
    α_L = 1 - α_G
    return(α_L)