is empty, are empty, is not empty and are not empty are used to identify cases that have or do not have specified attributes with values in a particular range. For example, the case:
egg 2 2 3 milk 12 15 18 soy 2 2 2 wheat 600 750 800
satisfies the conditions:
{egg, milk, soy, wheat} in range [1000, 10000] is empty
{egg, milk, soy, wheat} in range [10, 100] is not empty
at least 2 {egg, milk} in range [100, 1000] are empty
at least 2 {soy, wheat} in range [100, 1000] are not empty