$($define $($course$-$w$-$credits c credits$)$

$($cond

$[(>=($course$-$credit c$)$ credits$)$ ;;if the course has enough credits

$($cons c $($course$-$w$-$credits$--$loc $($course$-$dependents c$)$ credits$))]$ ; combine it and process dependents

$[$else

$($course$-$w$-$credits$--$loc $($course$-$dependents c$)$ credits$)]))$

$($define $($course$-$w$-$credits$--$loc loc credits$)$

$($cond

$[($empty$?$ loc$)$ empty$]$ ; base case: if the list is empty, return empty

$[$else

$($append $($course$-$w$-$credits $($first loc$)$ credits$)$ ;;process the first course associated with the credits

$($course$-$w$-$credits$--$loc $($rest loc$)$ credits$))]))$

$($define $($course$-$with$-$min$-$credits tree credits$)$

$($cond

$[($empty$?$ tree$)$ empty$]$ ; base case: if the tree is empty, return empty

$[($course$?$ tree$)($course$-$w$-$credits tree credits$)]$ ; if it's a single course, process it

$[($list$?$ tree$)($course$-$w$-$credits$--$loc tree credits$)]$ ; if it's a list of course with credits, process the list

$[$else $($error "Invalid input"$)]))$ ;;error handling for invalid inputs

the above code I have run but cannot return output, what wrong inside the function body??