
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 several numbers, the first number is denoted as $a_1$, the second number as $a_2$, the third number as $a_3$, ..., and the $n$-th number as $a_n$. If $a_1 = -0.5$, starting from the second number, each number is equal to the reciprocal of the difference between 1 and the number before it.  
(1) Calculate:  
$a_2 =$ ;  
$a_3 =$ ;  
$a_4 =$ .  
(2) Conjecture:  
$a_{1998} =$ ;  
$a_{2000} =$ .

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