use code of https://github.com/filterpaper/qmk_userspace

common/keymap.h

@@ -1,18 +1,5 @@
-/* Copyright 2022 Christoph Cullmann
- *
- * 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, see <http://www.gnu.org/licenses/>.
- */
+// Copyright Christoph Cullmann
+// SPDX-License-Identifier: GPL-2.0+
 
 // our layers
 enum my_layers {
@@ -63,25 +50,7 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 
 };
 
-#include "achordion.h"
-
-bool process_record_user(uint16_t keycode, keyrecord_t* record) {
-  if (!process_achordion(keycode, record)) { return false; }
-  return true;
-}
-
-void matrix_scan_user(void) {
-  achordion_task();
-}
-
-bool achordion_chord(uint16_t tap_hold_keycode,
-                     keyrecord_t* tap_hold_record,
-                     uint16_t other_keycode,
-                     keyrecord_t* other_record) {
-  // follow the opposite hands rule.
-  return on_left_hand(tap_hold_record->event.key) !=
-         on_left_hand(other_record->event.key);
-}
+#include "filterpaper.h"
 
 void keyboard_post_init_user(void) {
     // always use the same effect