On the left of the recursive equation we have n as the parameter, on the right hand side the function will appear within some expression however the call will be made to the function at n-1 rather than n . People often put 0 on the right hand side of the base case when they mean nil and vise versa. Think about the type of the output, if the result of the function should be a list then nil is commonly the base result. If the output is a number then the base case will be a number. This means that one of the equations implies that the output should be a list but other equation implies the output should be an integer.
People try to perform operations within the functions.
Remember you can only describe the output on the right hand side you are not writing instructions for the machine to carry out as you would in a traditional language. Missing parameters in the recursive call. Now go back and try the rest of the problems before getting the rest of the answers from here.