
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
Given the following propositions:

1. $y=1$ is a power function;
2. The function $f(x)=2^{x}-\log_{2}x$ has exactly one zero point;
3. The solution set of $\sqrt{x-1}(x-2)\geqslant 0$ is $[2,+\infty)$;
4. "$x < 1$" is a sufficient but not necessary condition for "$x < 2$";
5. The sequence $\{a_{n}\}$ whose first $n$ terms sum is $S_{n}$, and $S_{n}=a^{n}-1 (a\in R)$, is an arithmetic or geometric sequence;

The sequence number of the true proposition is _____ .

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