
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
Shift the graph of the function $y=\sin 2x- \sqrt {3}\cos 2x$ to the left by $\varphi (0 < \varphi \leqslant \frac {\pi}{2})$ units to obtain the graph of $f(x)$, and determine the range of $\varphi$ if $f(x)$ is monotonically decreasing on $\left( \frac {\pi}{4}, \frac {\pi}{2}\right)$.

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