diff --git a/extensions/fablabchemnitz/incadiff/incadiff.inx b/extensions/fablabchemnitz/incadiff/incadiff.inx
new file mode 100644
index 00000000..adefde53
--- /dev/null
+++ b/extensions/fablabchemnitz/incadiff/incadiff.inx
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<inkscape-extension xmlns="http://www.inkscape.org/namespace/inkscape/extension">
+    <name>Incadiff</name>
+    <id>fablabchemnitz.de.incadiff</id>
+    <effect needs-document="true" needs-live-preview="false">
+        <effects-menu hidden="false">
+            <submenu name="FabLab Chemnitz">
+                <submenu name="Modify existing Path(s)"/>
+            </submenu>
+        </effects-menu>
+        <menu-tip>Apply successive difference operations on superimposed paths. Useful for plotter addicts.</menu-tip>
+        <object-type>all</object-type>
+    </effect>
+    <script>
+        <command location="inx" interpreter="python">incadiff.py</command>
+    </script>
+</inkscape-extension>
\ No newline at end of file
diff --git a/extensions/fablabchemnitz/incadiff/incadiff.py b/extensions/fablabchemnitz/incadiff/incadiff.py
new file mode 100644
index 00000000..f01f3405
--- /dev/null
+++ b/extensions/fablabchemnitz/incadiff/incadiff.py
@@ -0,0 +1,359 @@
+#!/usr/bin/env python3
+# coding=utf-8
+
+"""
+Copyright (C) 2021 Thomas Maziere <thomas.maziere@incaya.fr>
+
+Largely and mostly inspired by inx-pathops (https://gitlab.com/moini_ink/inx-pathops/)
+Copyright (C) 2014  Ryan Lerch (multiple difference)
+              2016  Maren Hachmann <marenhachmannATyahoo.com>
+                    (refactoring, extend to multibool)
+              2017  su_v <suv-sf@users.sf.net>
+                    Rewrite to support large selections (process in chunks), to
+                    improve performance (support groups, z-sort ids with python
+                    instead of external query), and to extend GUI options.
+
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+"""
+
+"""
+incadiff
+Apply successive difference operations on superimposed paths. Useful for plotter addicts.
+"""
+
+import os
+from shutil import copy2
+import time
+from lxml import etree
+
+
+import inkex
+import inkex.command
+
+__version__ = '0.2'
+
+# Global "constants"
+SVG_SHAPES = ('rect', 'circle', 'ellipse', 'line', 'polyline', 'polygon')
+
+
+# ----- general helper functions
+
+def timed(f):
+    """Minimalistic timer for functions."""
+    # pylint: disable=invalid-name
+    start = time.time()
+    ret = f()
+    elapsed = time.time() - start
+    return ret, elapsed
+
+
+def get_inkscape_version():
+    ink = inkex.command.INKSCAPE_EXECUTABLE_NAME
+    try:  # needed prior to 1.1
+        ink_version = inkex.command.call(ink, '--version').decode("utf-8")
+    except AttributeError:  # needed starting from 1.1
+        ink_version = inkex.command.call(ink, '--version')
+
+    pos = ink_version.find("Inkscape ")
+    if pos != -1:
+        pos += 9
+    else:
+        return None
+    v_num = ink_version[pos:pos+3]
+    return(v_num)
+
+# ----- SVG element helper functions
+
+
+def get_defs(node):
+    """Find <defs> in children of *node*, return first one found."""
+    path = '/svg:svg//svg:defs'
+    try:
+        return node.xpath(path, namespaces=inkex.NSS)[0]
+    except IndexError:
+        return etree.SubElement(node, inkex.addNS('defs', 'svg'))
+
+
+def is_group(node):
+    """Check node for group tag."""
+    return node.tag == inkex.addNS('g', 'svg')
+
+
+def is_path(node):
+    """Check node for path tag."""
+    return node.tag == inkex.addNS('path', 'svg')
+
+
+def is_basic_shape(node):
+    """Check node for SVG basic shape tag."""
+    return node.tag in (inkex.addNS(tag, 'svg') for tag in SVG_SHAPES)
+
+
+def is_custom_shape(node):
+    """Check node for Inkscape custom shape type."""
+    return inkex.addNS('type', 'sodipodi') in node.attrib
+
+
+def is_shape(node):
+    """Check node for SVG basic shape tag or Inkscape custom shape type."""
+    return is_basic_shape(node) or is_custom_shape(node)
+
+
+def has_path_effect(node):
+    """Check node for Inkscape path-effect attribute."""
+    return inkex.addNS('path-effect', 'inkscape') in node.attrib
+
+
+def is_modifiable_path(node):
+    """Check node for editable path data."""
+    return is_path(node) and not (has_path_effect(node) or
+                                  is_custom_shape(node))
+
+
+def is_image(node):
+    """Check node for image tag."""
+    return node.tag == inkex.addNS('image', 'svg')
+
+
+def is_text(node):
+    """Check node for text tag."""
+    return node.tag == inkex.addNS('text', 'svg')
+
+
+def does_pathops(node):
+    """Check whether node is supported by Inkscape path operations."""
+    return (is_path(node) or
+            is_shape(node) or
+            is_text(node))
+
+
+# ----- list processing helper functions
+
+def recurse_selection(node, id_list, level=0, current=0):
+    """Recursively process selection, add checked elements to id list."""
+    current += 1
+    if not level or current <= level:
+        if is_group(node):
+            for child in node:
+                id_list = recurse_selection(child, id_list, level, current)
+    if does_pathops(node):
+        id_list.append(node.get('id'))
+    return id_list
+
+
+def z_sort(node, alist):
+    """Return new list sorted in document order (depth-first traversal)."""
+    ordered = []
+    id_list = list(alist)
+    count = len(id_list)
+    for element in node.iter():
+        element_id = element.get('id')
+        if element_id is not None and element_id in id_list:
+            id_list.remove(element_id)
+            ordered.append(element_id)
+            count -= 1
+            if not count:
+                break
+    return ordered
+
+
+def z_iter(node, alist):
+    """Return iterator over ids in document order (depth-first traversal)."""
+    id_list = list(alist)
+    for element in node.iter():
+        element_id = element.get('id')
+        if element_id is not None and element_id in id_list:
+            id_list.remove(element_id)
+            yield element_id
+
+
+def chunks(alist, max_len):
+    """Chunk a list into sublists of max_len length."""
+    for i in range(0, len(alist), max_len):
+        yield alist[i:i+max_len]
+
+
+class IncadiffExtension(inkex.Effect):
+
+    def __init__(self):
+        inkex.Effect.__init__(self)
+        self.actions_list = []
+
+    def add_arguments(self, pars):
+        pars.add_argument("--my_option", type=inkex.Boolean,
+                          help="An example option, put your options here")
+
+    def get_selected_ids(self):
+        """Return a list of valid ids for inkscape path operations."""
+        id_list = []
+        if len(self.svg.selected) == 0:
+            pass
+        else:
+            level = 0
+            for node in self.svg.selected.values():
+                recurse_selection(node, id_list, level)
+        if len(id_list) < 2:
+            inkex.errormsg("This extension requires at least 2 elements " +
+                           "of type path, shape or text. " +
+                           "The elements can be part of selected groups, " +
+                           "or directly selected.")
+            return None
+        if len(id_list) > 64:
+            inkex.errormsg("You should not select more than 64 shapes/paths, " +
+                           "and ideally you should apply this extension to small groups of objects.")
+            return None
+        
+        else:
+            return id_list
+
+    def get_sorted_ids(self):
+        """Return a list with z-sorted ids."""
+        sorted_ids = None
+        id_list = self.get_selected_ids()
+        if id_list is not None:
+            sorted_ids = list(z_iter(self.document.getroot(), id_list))
+            return (sorted_ids)
+        else:
+            return
+        
+
+    def run_cmd(self, tempfile):
+        #ink_version = get_inkscape_version()
+        self.actions_list.append("FileSave")
+        extra_param = "--batch-process"
+        # if ink_version == "1.0":
+        #     self.actions_list.append("FileQuit")
+        #     extra_param = "--with-gui"
+        actions = ";".join(self.actions_list)
+        inkex.command.inkscape(tempfile, extra_param, actions=actions)
+
+    def duplicate_and_diff(self, id_list, tempfile):
+        # for each selected path, duplicate and diff for each path below
+        nb_shapes = len(id_list)
+        for i in range(0, nb_shapes):
+            top_path = id_list[i]
+            j = i
+            while j > 0:
+                j -= 1
+                self.actions_list.append("select-by-id:"+top_path)
+                self.actions_list.append("EditDuplicate")
+                self.actions_list.append("select-by-id:" + id_list[j])
+                self.actions_list.append("SelectionDiff")
+                self.actions_list.append("EditDeselect")
+            if nb_shapes > 20:
+                self.run_cmd(tempfile)
+                self.actions_list = []
+        if len(self.actions_list) > 0:
+            self.run_cmd(tempfile)
+            self.actions_list = []
+
+    def loop_diff(self):
+        """Loop through selected items and run external command(s)."""
+
+        tempfile = self.options.input_file + "-incadiff.svg"
+        # prepare
+        # we need to do this because command line Inkscape with gui
+        # gives lots of info dialogs when the file extension isn't 'svg'
+        # so the inkscape() call cannot open the file without user
+        # interaction, and fails in the end when trying to save
+        copy2(self.options.input_file, tempfile)
+
+        # loop through selected paths
+        id_list = self.get_sorted_ids()
+        if id_list is not None:
+            self.duplicate_and_diff(id_list, tempfile)
+        else:
+            return
+
+        
+        # replace current document with content of temp copy file
+        self.document = inkex.load_svg(tempfile)
+        # update self.svg
+        self.svg = self.document.getroot()
+
+        # purge missing tagrefs (see below)
+        self.update_tagrefs()
+        # clean up
+        self.cleanup(tempfile)
+
+    def cleanup(self, tempfile):
+        """Clean up tempfile."""
+        try:
+            os.remove(tempfile)
+        except Exception:  # pylint: disable=broad-except
+            pass
+
+    def effect(self):
+        if self.has_tagrefs():
+            # unsafe to use with extensions ...
+            inkex.utils.errormsg("This document uses Inkscape selection sets. " +
+                                 "Modifying the content with this extension " +
+                                 "may cause Inkscape to crash on reload or close. " +
+                                 "Please delete the selection sets, " +
+                                 "save the document under a new name and " +
+                                 "try again in a new Inkscape session.")
+        else:
+            self.loop_diff()
+
+    def has_tagrefs(self):
+        """Check whether document has selection sets with tagrefs."""
+        defs = get_defs(self.document.getroot())
+        inkscape_tagrefs = defs.findall(
+            "inkscape:tag/inkscape:tagref", namespaces=inkex.NSS)
+        return len(inkscape_tagrefs) > 0
+
+    def update_tagrefs(self, mode='purge'):
+        """Check tagrefs for deleted objects."""
+        defs = get_defs(self.document.getroot())
+        inkscape_tagrefs = defs.findall(
+            "inkscape:tag/inkscape:tagref", namespaces=inkex.NSS)
+        if len(inkscape_tagrefs) > 0:
+            for tagref in inkscape_tagrefs:
+                href = tagref.get(inkex.addNS('href', 'xlink'))[1:]
+                if self.svg.getElementById(href) is None:
+                    if mode == 'purge':
+                        tagref.getparent().remove(tagref)
+                    elif mode == 'placeholder':
+                        temp = etree.Element(inkex.addNS('path', 'svg'))
+                        temp.set('id', href)
+                        temp.set('d', 'M 0,0 Z')
+                        self.document.getroot().append(temp)
+
+    # ----- workaround to fix Effect() performance with large selections
+
+    def collect_ids(self, doc=None):
+        """Iterate all elements, build id dicts (doc_ids, selected)."""
+        doc = self.document if doc is None else doc
+        id_list = list(self.options.ids)
+        for node in doc.getroot().iter(tag=etree.Element):
+            if 'id' in node.attrib:
+                node_id = node.get('id')
+                self.doc_ids[node_id] = 1
+                if node_id in id_list:
+                    self.svg.selected[node_id] = node
+                    id_list.remove(node_id)
+
+    def getselected(self):
+        """Overload Effect() method."""
+        self.collect_ids()
+
+    def getdocids(self):
+        """Overload Effect() method."""
+        pass
+
+
+if __name__ == '__main__':
+    IncadiffExtension().run()