
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
Given that $a \in A$, and $a-1 \notin A$ and $a+1 \notin A$, $a$ is called an isolated element of set $A$. How many four-element subsets of the set $M=\{1,2, \cdots, 9\}$ have no isolated elements?

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