
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 function $f(x)=|x-a|-|x-4|$, where $a\in \mathbb{R}$.  
(Ⅰ) When $a=-1$, find the solution set of the inequality $f(x) \geqslant 4$;  
(Ⅱ) If for all $x\in \mathbb{R}$, $|f(x)|\leqslant 2$ always holds, find the range of values for $a$.

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