Given the following definition for the length of a list

length(L)=ifL=<> then 0 else 1+length(tail(L))

What are the steps in evaluation of length (<r,s,t,u>)

Construct a recursive definition for the function

f(n)=floor(0/2)+floor(1/2)+...+floor(n/2)

and

f(n) = (0mod2)+(1mod3)+...+(n mod(n+2)).