Consider the functions double and palindrome, defined respectively as double $x=x^{**}2$

palindrome $xs=$ reverse $xs==xs$

$($a$)$ What is the type of double?

$($b$)$ What is the type of palindrome?

$($c$)$ Notice that there are certain type class constraints present in both types of double and palindrome. What is the reason for this, in either case?