
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
There are some phenomena in life:<br/>① Straightening a curved river channel shortens its length;<br/>② When two thin wooden strips are stacked together with both ends coinciding, if there is a gap in the middle, then both strips cannot be straight;<br/>③ When planting trees, as long as the positions of two tree pits are determined, the tree pits in the same row can be in a straight line;<br/>④ It only takes two nails to fix a thin wooden strip on the wall.<br/>The principle that can be explained by the basic fact "two points determine a straight line" is ____ (only fill in the numbers).

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