A database can be represented in Prolog as a set of facts.$$ For example, a database about families can be represented so that each family is described by one clause.$$ As the number of children varies from family to family the children are represented by a list that can accommodate any number of items. Each person is$,$ in turn, represented by a structure of four components:

$$

name, surname, date of birth, job. The job information is $$unemployed$\text{'},$ or it contains the name of the organization and the salary.

$$

$$

For instance:

$$

family$($

person$($tom$,$ fox, date$(7,$may,$1950),$ works$($bbc$,15200)),$

person$($ ann, fox, date$(9,$may, $1951),$ unemployed$),$

$[$ person$($pat$,$ fox, date$(5,$may,$1973),$unemployed$),$

person$($jim$,$ fox, date$($S$,$may,$1973),$ unemployed$)]).$

$$

$$

Write queries to find the following from the family database:

$($a$)$ names of families without children;

$($b$)$ all employed children;

$($c$)$ names of families with employed wives and unemployed husbands;

$($d$)$ all the children whose parents differ in age by at least $15$ years.