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docs/Advent_of_Code_2017_December_4th.md

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+
+# Advent of Code 2017
+
+## December 4th
+To ensure security, a valid passphrase must contain no duplicate words.
+
+For example:
+
+* aa bb cc dd ee is valid.
+* aa bb cc dd aa is not valid - the word aa appears more than once.
+* aa bb cc dd aaa is valid - aa and aaa count as different words.
+
+The system's full passphrase list is available as your puzzle input. How many passphrases are valid?
+
+
+```python
+from notebook_preamble import J, V, define
+```
+
+I'll assume the input is a Joy sequence of sequences of integers.
+
+    [[5 1 9 5]
+     [7 5 4 3]
+     [2 4 6 8]]
+
+So, obviously, the initial form will be a `step` function:
+
+    AoC2017.4 == 0 swap [F +] step
+
+
+    F == [size] [unique size] cleave =
+
+
+The `step_zero` combinator includes the `0 swap` that would normally open one of these definitions:
+
+
+```python
+J('[step_zero] help')
+```
+
+    0 roll> step
+    
+
+
+    AoC2017.4 == [F +] step_zero
+
+
+```python
+define('AoC2017.4 == [[size] [unique size] cleave = +] step_zero')
+```
+
+
+```python
+J('''
+
+[[5 1 9 5]
+ [7 5 4 3]
+ [2 4 6 8]] AoC2017.4
+
+''')
+```
+
+    2
+