But why?

So plus operator is concat

plus

Returns a list containing all elements of the original collection and then all elements of the given elements sequence.

plusElement

Returns a list containing all elements of the original collection and then the given element.

Yes... I understand how it happend. But it was postfactum, after type inference gave me

List<Any>

instead of

List<List<Int>>

. And I'd prefer to know exactly what's happening when I type it 😒imple_smile: . I'm wondering if better names could have been used.

It seems so. It works correctly when you extract variable and use intention action to set explicit type.