
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
In the tetrahedron $OABC$, given that $\overrightarrow {OA} = \overrightarrow {a}, \overrightarrow {OB} = \overrightarrow {b}$, and $\overrightarrow {OC} = \overrightarrow {c}$, where $D$ is the midpoint of $AB$ and $M$ is the midpoint of $CD$, express $\overrightarrow {CM}$ in terms of $\overrightarrow {a}$, $\overrightarrow {b}$, and $\overrightarrow {c}$.

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