This is called the maximum independent set problem, though I like the social distancing name

@pajonk I've added a paragraph explaining that. Basically it only happens for empty lists (that the starting bracket doesn't have an index).

Personally, I think that the last two examples (from a UI standpoint) should be < 1 2 3 [4] 5 ... 11 > and < 1 ... 6 [7] 8 ... 11 >. Regardless, you should clarify if there is some priority for how numbers should be distributed (e.g. should the center have more numbers?)

As challenges should be self-contained, I suggest you add the mathematical definition from my post (and maybe an informal explanation of how the rules are applied non-deterministically)