diff --git a/cv4/list_ops.c b/cv4/list_ops.c
index 11168cd..4350f85 100644
--- a/cv4/list_ops.c
+++ b/cv4/list_ops.c
@@ -18,7 +18,7 @@ list_t *new_list(size_t length, list_element_t elements[]) {
 
 list_t *append_list(list_t *list1, list_t *list2)
 {
-    size_t length = list1->length + list2->length;
+    size_t length = (list1->length + list2->length);
     list_t *list3 = new_list(list1->length + list2->length,list1->elements);
     list3->length = length;
     for (size_t i = list1->length; i < list3->length; i++)
@@ -27,7 +27,7 @@ list_t *append_list(list_t *list1, list_t *list2)
 }
 
 list_t *filter_list(list_t *list, bool (*predicate)(list_element_t)) {
-   list_element_t filter[list->length];
+   list_element_t *filter[list->length];
    size_t filter_length = 0;
    for(size_t i = 0; i < list->length;i++){
      if(predicate(list->elements[i])){
@@ -49,19 +49,16 @@ size_t length_list(list_t *list) {
 
 list_t *map_list(list_t *list, list_element_t (*mapper)(list_element_t)) {
     list_t *result = new_list(list->length, list->elements);
-    if (result == NULL) {
+     if (result == NULL) {
         return NULL; 
     }
-
-    for (size_t i = 0; i < list->length; i++) {
+	for (size_t i = 0; i < list->length; i++) {
         result->elements[i] = mapper(list->elements[i]);
     }
 
     return result;
 }
 
-
-
 list_element_t foldl_list(list_t *list, list_element_t initial, list_element_t (*folder)(list_element_t, list_element_t)) {
     list_element_t result = initial;
     for (size_t i = 0; i < list->length; i++) {