diff --git a/README.md b/README.md
index 2685e7a..27d019f 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
# Christoph Cullmann's Layout
-Layout with 42 keys, using Dhorf as base layer:
+Layout with 42 keys based on Miryoku, using Dhorf as base layer:
dhorf (Oxey)
v l h k q j f o u ,
@@ -24,10 +24,8 @@ ATM this needs to be cloned to
to work properly.
-Based on
+Based on ideas and code from:
-https://oxey.dev/dhorf
-
-and
-
-https://github.com/manna-harbour/miryoku
+- https://oxey.dev/dhorf
+- https://github.com/manna-harbour/miryoku
+- https://getreuer.info/posts/keyboards/achordion
diff --git a/common/config.h b/common/config.h
index 53db981..7d459d8 100644
--- a/common/config.h
+++ b/common/config.h
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
#pragma once
diff --git a/common/keymap.h b/common/keymap.h
index ef49bf5..09cb192 100644
--- a/common/keymap.h
+++ b/common/keymap.h
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
// our layers
diff --git a/crkbd/config.h b/crkbd/config.h
index ac17ea4..100d602 100644
--- a/crkbd/config.h
+++ b/crkbd/config.h
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
#pragma once
diff --git a/crkbd/keymap.c b/crkbd/keymap.c
index 52a1ec0..74ef914 100644
--- a/crkbd/keymap.c
+++ b/crkbd/keymap.c
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
#include QMK_KEYBOARD_H
diff --git a/planck/config.h b/planck/config.h
index 9093362..e1a1763 100644
--- a/planck/config.h
+++ b/planck/config.h
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
#pragma once
diff --git a/planck/keymap.c b/planck/keymap.c
index 2666e77..854537b 100644
--- a/planck/keymap.c
+++ b/planck/keymap.c
@@ -1,17 +1,6 @@
-/* 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 .
+/**
+ * SPDX-FileCopyrightText: 2024 Christoph Cullmann
+ * SPDX-License-Identifier: GPL-2.0-or-later
*/
#include QMK_KEYBOARD_H