diff --git a/sose2021/r/w03/P03-1.R b/sose2021/r/w03/P03-1.R
index 19151e3..54ef103 100644
--- a/sose2021/r/w03/P03-1.R
+++ b/sose2021/r/w03/P03-1.R
@@ -1,3 +1,5 @@
+# Josua Kugler, Christian Merten
+
 `%o%` <- function(f, g) {
     comp <- function(...) {
         return(f(g(...)))
diff --git a/sose2021/r/w03/P03-2.R b/sose2021/r/w03/P03-2.R
index 32cc5de..790c821 100644
--- a/sose2021/r/w03/P03-2.R
+++ b/sose2021/r/w03/P03-2.R
@@ -1,3 +1,5 @@
+# Josua Kugler, Christian Merten
+
 n_diag <- function(mat, n) {
     stopifnot("Matrix not quadratic" = nrow(mat) == ncol(mat))
     stopifnot("Matrix does not have such a (sub)diagonal" = abs(n) < nrow(mat))
diff --git a/sose2021/r/w03/P03-3.R b/sose2021/r/w03/P03-3.R
index a671d8f..2549c08 100644
--- a/sose2021/r/w03/P03-3.R
+++ b/sose2021/r/w03/P03-3.R
@@ -1,3 +1,5 @@
+# Josua Kugler, Christian Merten
+
 ## 1.
 
 size <- function(mat) {
@@ -98,16 +100,8 @@ is_solution_of <- function(s, s_star) {
 
 print_non_valid <- function(s, print_missing=T) {
     stopifnot("s is not a sudoku!" = is_sudoku(s))
-    s <- ""
     if (print_missing) {
-        missing_fields <- which(is.na(s), arr.ind=T)
-        if (nrow(missing_fields) > 0)
-            sapply(1:nrow(missing_fields), function(r) cat("missing value at ",
-                                                           missing_fields[r,1],
-                                                           ",",
-                                                           missing_fields[r,2],
-                                                           "\n",
-                                                           sep=""))
+        apply(which(is.na(s), arr.ind=T), 1, function(x) cat("missing value at ", x[1], ",", x[2], "\n", sep=""))
     }
     n <- size(s)[1]
     m <- size(s)[2]
@@ -132,7 +126,7 @@ print_non_valid <- function(s, print_missing=T) {
                                                        " is invalid\n",
                                                        sep=""))
     }
-    return(NULL)
+    invisible(NULL)
 }