a$)$ Complete the following function to return number of occurences of the first parameter in the second parameter list. occurs $1[1,2,3,1,2]$ will return $2$ since $1$ has $2$ occurrences in the list. occurs $3[1,2,3,1,2]$ will return $1$ and occurs $4[1,2,3,1,2]$ will return $0.$

occurs $-[]=0$

occurs a $(x$:$x5)=1$ et rest$=$occurs a $xs$

in if $a==x$ then

else

b$)$ Complete the following function to return number of occurences of the first parameter in the nodes of the second parameter tree. The definition of tree is given below. In the sample tree $t$ the calls return the corressponding values:

occurst $1t6$

occurst $2t2$

occurst $3t1$

occurst $4t0$

data Tree a $=$ Node $($a$,$ Tree a$,$ Tree a$)$ I Empty deriving Show

occurst $-$ Empty $=0$

occurst a $($Node $,$ left, right