2 3

```
2 4
```

Think, what does this mean? This means that there is a sub-sequence ending at index 2 such that if we add 1 element to it, we get a sequence ending at index 3, and index 4 respectively.

But, in case of 1 2 1 1, the sub-sequence would be {1 2 1} or {2 1} (depending on starting index). In this case, we cannot have an edge 2,4 , reason being in definition of function.

If we have a sub-sequence starting at index i,then f(i) is the minimum i at which this sub sequence ends. So, for f{1,2,1} and f{2,1}, the minimum i is 3, not 4. So there no edge from 2 to 4 is possible.

In short, if you have an edge from 2 to 3 and 2 to 4, this implies that element at 3 and 4 MUST be different.