
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Let $\overrightarrow {e_{1}}$ and $\overrightarrow {e_{2}}$ be two non-collinear vectors. Given $\overrightarrow {AB} = 2\overrightarrow {e_{1}} + k\overrightarrow {e_{2}}$, $\overrightarrow {BC} = \overrightarrow {e_{1}} + 3\overrightarrow {e_{2}}$, $\overrightarrow {CD} = 2\overrightarrow {e_{1}} - \overrightarrow {e_{2}}$, if points A, B, and D are collinear, find the value of $k$.

Present the answer in LaTex format: \boxed{Your answer}
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