diff --git a/README.md b/README.md
index 29d796a..6fbc7a7 100644
--- a/README.md
+++ b/README.md
@@ -1,21 +1,31 @@
-# Sudoku verifier
+# Validate a Sudoku
 
 ## Definition
-Sudokus are logic number puzzles in which cells in a 9×9 grid must be populated with 
-the digits 1 to 9 in a way that each digit occurrs only once in each unit (that is column, 
-row or block = 3×3 sub grid).
+Sudokus are number-puzzles in which cells in a 9×9 grid must be populated with the numbers `1` to `9`.
+
+The following constraints must apply to the 9×9 grid.
+
+ * Each digit from `1` to `9` only occurs only once 
+    * per row
+    * per column
+    * per block (i.e. 3×3 sub grid)
 
 ![a solved simple sudoku](sudoku.gif)
 
 ## Goal
-Validate if a given solution for a Sudoku is valid, by checking that the digit
-1 to 9 appear only once in column, in each row and in each of the 9 sub grids.
+Validate, if a given Sudoku is a valid solution. 
+
+The Sudoku must comply with the definition above.
 
 ### Input
-a sequence of 81 digits, organized in 9 columns and 9 rows
+A sequence of 81 digits, organized in 9 columns and 9 rows.
+
+The columns of a row are separated by blanks.
+
+Rows are separated by line-breaks.
 
 ### Output
-A boolean value, if the grid is valid.
+A boolean value `true` or `false` defining the correctness of the input.
 
 ### Constraints
 1 <= `digit` <= 9
diff --git a/src/test/resources/sudoku6.txt b/src/test/resources/sudoku6.txt
new file mode 100644
index 0000000..5aa6860
--- /dev/null
+++ b/src/test/resources/sudoku6.txt
@@ -0,0 +1,9 @@
+1 7 2 5 4 9 6 8 3
+6 4 5 8 7 3 2 1 9
+3 8 9 2 6 1 7 4 5
+4 9 6 3 2 7 8 5 1
+8 1 3 4 5 6 9 7 2
+2 5 7 1 9 8 4 3 6
+9 6 4 7 1 5 3 2 8
+7 3 1 6 8 2 5 9 4
+5 2 8 9 3 4 1 6 7
\ No newline at end of file
diff --git a/src/test/resources/sudoku7.txt b/src/test/resources/sudoku7.txt
new file mode 100644
index 0000000..42519d4
--- /dev/null
+++ b/src/test/resources/sudoku7.txt
@@ -0,0 +1,9 @@
+9 5 7 6 1 3 2 8 4
+4 8 3 2 5 7 1 9 6
+6 1 2 8 4 9 5 3 7
+1 7 8 3 6 4 9 5 2
+5 2 4 9 7 1 3 6 8
+3 6 9 5 2 8 7 4 1
+8 4 5 7 9 2 6 1 3
+2 9 1 4 3 6 8 7 5
+7 3 6 1 8 5 4 2 9
\ No newline at end of file
diff --git a/src/test/resources/sudoku8.txt b/src/test/resources/sudoku8.txt
new file mode 100644
index 0000000..fed9899
--- /dev/null
+++ b/src/test/resources/sudoku8.txt
@@ -0,0 +1,9 @@
+1 7 2 5 4 9 6 8 3
+6 4 5 8 7 3 2 1 9
+3 8 9 2 6 1 7 4 5
+4 9 6 3 2 7 8 5 1
+8 1 3 4 5 6 9 7 2
+2 5 7 1 9 8 4 3 6
+9 6 4 7 2 5 3 2 8
+7 3 1 6 8 2 5 9 4
+5 2 8 9 3 4 1 6 7
\ No newline at end of file
diff --git a/src/test/resources/testdata.csv b/src/test/resources/testdata.csv
index 788cdbd..2979be3 100644
--- a/src/test/resources/testdata.csv
+++ b/src/test/resources/testdata.csv
@@ -3,3 +3,6 @@ sudoku2.txt, true
 sudoku3.txt, false
 sudoku4.txt, true
 sudoku5.txt, false
+sudoku6.txt, true
+sudoku7.txt, true
+sudoku8.txt, false
\ No newline at end of file