
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
Among the following propositions:  
① The function $y= \sqrt {x^{2}-1} + \sqrt {1-x^{2}}$ is an even function, but not an odd function;  
② The condition “$\begin{cases} \left.\begin{matrix}a＞0 \\ \Delta=b^{2}-4ac\leq0\end{matrix}\right.\end{cases}$” is necessary and sufficient for “the solution set of the quadratic inequality $ax^2+bx+c\geq0$ is $\mathbb{R}$”;  
③ If the function $y=f(x)$ is defined on $\mathbb{R}$, then the graphs of $y=f(1-x)$ and $y=f(x-1)$ are symmetric about the y-axis;  
④ If the function $y=A\cos(\omega x+\varphi)$ ($A\neq0$) is an odd function, then $\varphi= \frac {\pi}{2}+k\pi$ ($k\in\mathbb{Z}$);  
⑤ Given $x\in(0,\pi)$, then the minimum value of $y=\sin x+ \frac {2}{\sin x}$ is $2\sqrt {2}$.  
Among these, the correct ones are \_\_\_\_\_\_.

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