
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 four propositions, the true proposition is __________.  
① The line passing through a fixed point P<sub>0</sub> (x<sub>0</sub>, y<sub>0</sub>) can be represented by the equation y-y<sub>0</sub> = k(x-x<sub>0</sub>)  
② The line passing through any two different points P<sub>1</sub> (x<sub>1</sub>, y<sub>1</sub>), P<sub>2</sub> (x<sub>2</sub>, y<sub>2</sub>) can be represented by the equation (y-y<sub>1</sub>)(x<sub>2</sub>-x<sub>1</sub>) = (x-x<sub>1</sub>)(y<sub>2</sub>-y<sub>1</sub>)  
③ The line not passing through the origin can be represented by the equation $$\frac {x}{a}+ \frac {y}{b}=1$$  
④ The line passing through a fixed point A (0, b) can be represented by the equation y = kx + b.

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