
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
(1) Use the Euclidean algorithm to find the greatest common divisor (GCD) of 840 and 1764.  
(2) Use the method of successive subtraction to find the greatest common divisor (GCD) of 561 and 255.

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