diff -r 21274e5950af -r a1f4cb076d2f src/ucx/list.c
--- a/src/ucx/list.c	Tue Aug 13 22:14:32 2019 +0200
+++ b/src/ucx/list.c	Sat Sep 24 16:26:10 2022 +0200
@@ -1,7 +1,7 @@
 /*
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
  *
- * Copyright 2016 Olaf Wintermann. All rights reserved.
+ * Copyright 2017 Mike Becker, Olaf Wintermann All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -26,13 +26,13 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "list.h"
+#include "ucx/list.h"
 
-UcxList *ucx_list_clone(UcxList *l, copy_func fnc, void *data) {
+UcxList *ucx_list_clone(const UcxList *l, copy_func fnc, void *data) {
     return ucx_list_clone_a(ucx_default_allocator(), l, fnc, data);
 }
 
-UcxList *ucx_list_clone_a(UcxAllocator *alloc, UcxList *l,
+UcxList *ucx_list_clone_a(UcxAllocator *alloc, const UcxList *l,
         copy_func fnc, void *data) {
     UcxList *ret = NULL;
     while (l) {
@@ -77,6 +77,7 @@
 }
 
 void ucx_list_free_content(UcxList* list, ucx_destructor destr) {
+    if (!destr) destr = free;
     while (list != NULL) {
         destr(list->data);
         list = list->next;
@@ -171,7 +172,8 @@
     return (UcxList*)(index == 0 ? e : NULL);
 }
 
-ssize_t ucx_list_find(UcxList *l, void *elem, cmp_func fnc, void *cmpdata) {
+ssize_t ucx_list_find(const UcxList *l, void *elem,
+        cmp_func fnc, void *cmpdata) {
     ssize_t index = 0;
     UCX_FOREACH(e, l) {
         if (fnc) {
@@ -188,7 +190,8 @@
     return -1;
 }
 
-int ucx_list_contains(UcxList *l, void *elem, cmp_func fnc, void *cmpdata) {
+int ucx_list_contains(const UcxList *l, void *elem,
+        cmp_func fnc, void *cmpdata) {
     return ucx_list_find(l, elem, fnc, cmpdata) > -1;
 }
 
@@ -205,15 +208,15 @@
     return s;
 }
 
-static UcxList *ucx_list_sort_merge(int length,
-        UcxList* restrict ls, UcxList* restrict le, UcxList* restrict re,
+static UcxList *ucx_list_sort_merge(size_t length,
+        UcxList* ls, UcxList* le, UcxList* re,
         cmp_func fnc, void* data) {
 
     UcxList** sorted = (UcxList**) malloc(sizeof(UcxList*)*length);
     UcxList *rc, *lc;
 
     lc = ls; rc = le;
-    int n = 0;
+    size_t n = 0;
     while (lc && lc != le && rc != re) {
         if (fnc(lc->data, rc->data, data) <= 0) {
             sorted[n] = lc;
@@ -254,9 +257,9 @@
     }
 
     UcxList *lc;
-    int ln = 1;
+    size_t ln = 1;
 
-    UcxList *restrict ls = l, *restrict le, *restrict re;
+    UcxList *ls = l, *le, *re;
     
     // check how many elements are already sorted
     lc = ls;
@@ -270,7 +273,7 @@
         return l; // this list is already sorted :)
     } else {
         UcxList *rc;
-        int rn = 1;
+        size_t rn = 1;
         rc = le;
         // skip already sorted elements
         while (rc->next != NULL && fnc(rc->next->data, rc->data, data) > 0) {
@@ -333,3 +336,93 @@
     alfree(alloc, e);
     return l;
 }
+
+
+static UcxList* ucx_list_setoperation_a(UcxAllocator *allocator,
+        UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata,
+        int op) {
+    
+    UcxList *res = NULL;
+    UcxList *cur = NULL;
+    const UcxList *src = left;
+    
+    do {
+        UCX_FOREACH(node, src) {
+            void* elem = node->data;
+            if (
+                (op == 0 && !ucx_list_contains(res, elem, cmpfnc, cmpdata)) ||
+                (op == 1 && ucx_list_contains(right, elem, cmpfnc, cmpdata)) ||
+                (op == 2 && !ucx_list_contains(right, elem, cmpfnc, cmpdata))) {
+                UcxList *nl = almalloc(allocator, sizeof(UcxList));
+                nl->prev = cur;
+                nl->next = NULL;
+                if (cpfnc) {
+                    nl->data = cpfnc(elem, cpdata);
+                } else {
+                    nl->data = elem;
+                }
+                if (cur != NULL)
+                    cur->next = nl;
+                cur = nl;
+                if (res == NULL)
+                    res = cur;
+            }
+        }
+        if (op == 0 && src == left)
+            src = right;
+        else
+            src = NULL;
+    } while (src != NULL);
+    
+    return res;
+}
+
+UcxList* ucx_list_union(UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    return ucx_list_union_a(ucx_default_allocator(),
+            left, right, cmpfnc, cmpdata, cpfnc, cpdata);
+}
+
+UcxList* ucx_list_union_a(UcxAllocator *allocator,
+        UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    
+    return ucx_list_setoperation_a(allocator, left, right,
+            cmpfnc, cmpdata, cpfnc, cpdata, 0);
+}
+
+UcxList* ucx_list_intersection(UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    return ucx_list_intersection_a(ucx_default_allocator(), left, right,
+            cmpfnc, cmpdata, cpfnc, cpdata);
+}
+
+UcxList* ucx_list_intersection_a(UcxAllocator *allocator,
+        UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    
+    return ucx_list_setoperation_a(allocator, left, right,
+            cmpfnc, cmpdata, cpfnc, cpdata, 1);
+}
+
+UcxList* ucx_list_difference(UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    return ucx_list_difference_a(ucx_default_allocator(), left, right,
+            cmpfnc, cmpdata, cpfnc, cpdata);
+}
+
+UcxList* ucx_list_difference_a(UcxAllocator *allocator,
+        UcxList const *left, UcxList const *right,
+        cmp_func cmpfnc, void* cmpdata,
+        copy_func cpfnc, void* cpdata) {
+    
+    return ucx_list_setoperation_a(allocator, left, right,
+            cmpfnc, cmpdata, cpfnc, cpdata, 2);
+}