
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
For natural numbers $a$ and $b$, a new operation $\nabla$ is defined such that $a \nabla b$ equals the sum of $b$ consecutive natural numbers starting from $a$. For example, $2 \nabla 3 = 2 + 3 + 4 = 9$, and $5 \nabla 4 = 5 + 6 + 7 + 8 = 26$. Evaluate $2 \nabla[0 \nabla(1 \nabla 7)]$.

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