copy over the copyright header
diff --git a/include/common.h b/include/common.h
index 008419d..e196da5 100644
--- a/include/common.h
+++ b/include/common.h
@@ -1,4 +1,22 @@
+/*
+ * BZip3 - A spiritual successor to BZip2.
+ * Copyright (C) 2022 Kamila Szewczyk
+ *
+ * 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 3 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/>.
+ */
+
#ifndef _COMMON_H
#define _COMMON_H
diff --git a/include/libbz3.h b/include/libbz3.h
index 12b907b..bde29f2 100644
--- a/include/libbz3.h
+++ b/include/libbz3.h
@@ -1,4 +1,22 @@
+/*
+ * BZip3 - A spiritual successor to BZip2.
+ * Copyright (C) 2022 Kamila Szewczyk
+ *
+ * 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 3 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/>.
+ */
+
#ifndef _LIBBZ3_H
#define _LIBBZ3_H
diff --git a/include/txt.h b/include/txt.h
index ef92a03..eac6d12 100644
--- a/include/txt.h
+++ b/include/txt.h
@@ -1,4 +1,22 @@
+/*
+ * BZip3 - A spiritual successor to BZip2.
+ * Copyright (C) 2022 Kamila Szewczyk
+ *
+ * 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 3 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/>.
+ */
+
#ifndef _TXT_H
#define _TXT_H
diff --git a/src/libbz3.c b/src/libbz3.c
index 51d5da0..aa671c1 100644
--- a/src/libbz3.c
+++ b/src/libbz3.c
@@ -1,4 +1,22 @@
+/*
+ * BZip3 - A spiritual successor to BZip2.
+ * Copyright (C) 2022 Kamila Szewczyk
+ *
+ * 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 3 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/>.
+ */
+
#include "libbz3.h"
#include <arpa/inet.h>
diff --git a/src/txt.c b/src/txt.c
index 316d04f..7c651aa 100644
--- a/src/txt.c
+++ b/src/txt.c
@@ -1,4 +1,22 @@
+/*
+ * BZip3 - A spiritual successor to BZip2.
+ * Copyright (C) 2022 Kamila Szewczyk
+ *
+ * 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 3 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/>.
+ */
+
#include "txt.h"
#include <math.h>
