Question $2$: $(20$ points for each case$)$

Write a predicate replace$/4$ that substitutes the first argument $x$ with the second argument $Y$ for the all the occurrences of $x$ in a list of elements. If the list is empty the result is the empty list. If $x$ is not in the list, then the result is the list itself.

Three cases

The list is empty, then the result is empty

$x$ matches the head, insert $Y$ in the new list and replace $x$ with $Y$ in the tail

$x$ does not match the head, replace $x$ in the tail

$?-$ replace$(1,6,[5,0,1,1,1,5,1],R.$

$R=[5,0,6,6,6,5,6]$

$?-$ replace$(a,z,[a,b,c,a,r,a,z],R.$

$R=[z,b,c,z,r,z,z].$