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deleted file mode 100644
index 15a15b2..0000000
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@@ -1,4 +0,0 @@
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deleted file mode 100644
index 5dc0e56..0000000
--- a/handin_1/look_up.py/.idea/inspectionProfiles/Project_Default.xml
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@@ -1,22 +0,0 @@
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deleted file mode 100644
index 6711606..0000000
--- a/handin_1/look_up.py/.idea/look_up.py.iml
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@@ -1,11 +0,0 @@
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deleted file mode 100644
index 37d8a93..0000000
--- a/handin_1/look_up.py/.idea/misc.xml
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@@ -1,10 +0,0 @@
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deleted file mode 100644
index 41b2a07..0000000
--- a/handin_1/look_up.py/.idea/modules.xml
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@@ -1,8 +0,0 @@
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deleted file mode 100644
index 7bd7add..0000000
--- a/handin_1/look_up.py/.idea/workspace.xml
+++ /dev/null
@@ -1,169 +0,0 @@
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-  <component name="FileTemplateManagerImpl">
-    <option name="RECENT_TEMPLATES">
-      <list>
-        <option value="Python Script" />
-      </list>
-    </option>
-  </component>
-  <component name="IdeDocumentHistory">
-    <option name="CHANGED_PATHS">
-      <list>
-        <option value="$PROJECT_DIR$/look_up.py" />
-      </list>
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-  <component name="ProjectFrameBounds">
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-  <component name="ProjectView">
-    <navigator proportions="" version="1">
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-    <panes>
-      <pane id="ProjectPane">
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-          <expand>
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diff --git a/handin_1/look_up.py/look_up.py b/handin_1/look_up.py/look_up.py
deleted file mode 100644
index 510a910..0000000
--- a/handin_1/look_up.py/look_up.py
+++ /dev/null
@@ -1,90 +0,0 @@
-table =\
-    {
-        'O-': {
-            'O-': True,
-            'O+': True,
-            'A-': True,
-            'A+': True,
-            'B-': True,
-            'B+': True,
-            'AB-': True,
-            'AB+': True
-    },
-        'O+': {
-            'O-': False,
-            'O+': True,
-            'A-': False,
-            'A+': True,
-            'B-': False,
-            'B+': True,
-            'AB-': False,
-            'AB+': True
-        },
-        'A-': {
-            'O-': False,
-            'O+': False,
-            'A-': True,
-            'A+': True,
-            'B-': False,
-            'B+': False,
-            'AB-': True,
-            'AB+': True
-        },
-        'A+': {
-            'O-': False,
-            'O+': False,
-            'A-': False,
-            'A+': True,
-            'B-': False,
-            'B+': False,
-            'AB-': False,
-            'AB+': True
-        },
-        'B-': {
-            'O-': False,
-            'O+': False,
-            'A-': False,
-            'A+': False,
-            'B-': True,
-            'B+': True,
-            'AB-': True,
-            'AB+': True
-        },
-        'B+': {
-            'O-': False,
-            'O+': False,
-            'A-': False,
-            'A+': False,
-            'B-': False,
-            'B+': True,
-            'AB-': False,
-            'AB+': True
-        },
-        'AB-': {
-            'O-': False,
-            'O+': False,
-            'A-': False,
-            'A+': False,
-            'B-': False,
-            'B+': False,
-            'AB-': True,
-            'AB+': True
-        },
-        'AB+': {
-            'O-': False,
-            'O+': False,
-            'A-': False,
-            'A+': False,
-            'B-': False,
-            'B+': False,
-            'AB-': False,
-            'AB+': True
-        }
-}
-
-
-def look_up(donor, rec):
-    return table[donor][rec]
-
-
-print(look_up('A-', 'O-'))
diff --git a/week1.py b/week1.py
new file mode 100644
index 0000000..57c0ff0
--- /dev/null
+++ b/week1.py
@@ -0,0 +1,123 @@
+import itertools
+from enum import unique, Enum
+
+
+@unique
+class BloodType(Enum):
+    O_NEGATIVE = (0, 0, 0)  # (a, b, sign)
+    O_POSITIVE = (0, 0, 1)
+    A_NEGATIVE = (1, 0, 0)
+    A_POSITIVE = (1, 0, 1)
+    B_NEGATIVE = (0, 1, 0)
+    B_POSITIVE = (0, 1, 1)
+    AB_NEGATIVE = (1, 1, 0)
+    AB_POSITIVE = (1, 1, 1)
+
+
+def blood_cell_compatibility_lookup(recipient: BloodType, donor: BloodType) -> bool:
+    """
+    https://en.wikipedia.org/wiki/Blood_type#Red_blood_cell_compatibility
+    """
+    return {
+        BloodType.O_NEGATIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: False,
+            BloodType.A_NEGATIVE: False,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: False,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.O_POSITIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: True,
+            BloodType.A_NEGATIVE: False,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: False,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.A_NEGATIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: False,
+            BloodType.A_NEGATIVE: True,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: False,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.A_POSITIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: True,
+            BloodType.A_NEGATIVE: True,
+            BloodType.A_POSITIVE: True,
+            BloodType.B_NEGATIVE: False,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.B_NEGATIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: False,
+            BloodType.A_NEGATIVE: False,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: True,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.B_POSITIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: True,
+            BloodType.A_NEGATIVE: False,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: True,
+            BloodType.B_POSITIVE: True,
+            BloodType.AB_NEGATIVE: False,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.AB_NEGATIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: False,
+            BloodType.A_NEGATIVE: True,
+            BloodType.A_POSITIVE: False,
+            BloodType.B_NEGATIVE: True,
+            BloodType.B_POSITIVE: False,
+            BloodType.AB_NEGATIVE: True,
+            BloodType.AB_POSITIVE: False
+        },
+        BloodType.AB_POSITIVE: {
+            BloodType.O_NEGATIVE: True,
+            BloodType.O_POSITIVE: True,
+            BloodType.A_NEGATIVE: True,
+            BloodType.A_POSITIVE: True,
+            BloodType.B_NEGATIVE: True,
+            BloodType.B_POSITIVE: True,
+            BloodType.AB_NEGATIVE: True,
+            BloodType.AB_POSITIVE: True
+        },
+    }[recipient][donor]
+
+
+def blood_cell_compatibility_boolean(recipient: BloodType, donor: BloodType) -> bool:
+    (ra, rb, rs), (da, db, ds) = recipient.value, donor.value
+    
+    return (ra or not da) and (rb or not db) and (rs or not ds)
+
+
+if __name__ == '__main__':
+    green = 0
+    red = 0
+    for recipient, donor in itertools.product(BloodType, repeat=2):
+        lookup = blood_cell_compatibility_lookup(recipient, donor)
+        boolean = blood_cell_compatibility_boolean(recipient, donor)
+        if lookup == boolean:
+            green += 1
+        else:
+            print(f"'{BloodType(donor).name} -> {BloodType(recipient).name}' should be {lookup}.")
+            red += 1
+    print("Green:", green)
+    print("Red  :", red)