
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
The number of incorrect statements about vectors among the following is _______.

① If vectors $\overrightarrow {AB}$ and $\overrightarrow {CD}$ are collinear, then the four points A, B, C, and D must lie on the same straight line.  
② All unit vectors are equal.  
③ Any vector is not equal to its opposite vector.  
④ Quadrilateral ABCD is a parallelogram if and only if $\overrightarrow {AB} = \overrightarrow {DC}$.

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