$2)$ Consider the Employee database of Figure $1.$ Give a relational algebra expression to perform each of the following queries:

$-$ Find the name of each employee who lives in city $$Dallas$.$

$\backslash$Pi $($person$\_$name$)(\backslash$sigma $($city$=$Dallas$)($employee$))$

$-$ Find the name of each employee who lives in $$Dallas$$ and whose salary is greater than $$100000$

$\backslash$Pi $($person$\_$name$)(\backslash$sigma $($city$=$Dallas$$ salary$>100000)($employee x works$))$

$-$ Find the name of each employee who does not work for $$BigDallas$$