Set notation.Use the filter and$/$or map notations to concisely

express the following sets

$($a$)$ The set of all composite natural numbers. $\{0,4,6,8,9,10,12,14,15,16,18,20,...\}.$

$($b$)$ The set of all straight lines in the Cartesian plane. $($Con$-$

sider a straight line to be a suitable subset of R $\backslash$times R$.)$