[Grammar] "each other" vs "one another"

[KEN JPN]

"each other" vs "one another"

When I was still a student, I learned that
1, "each other" is used between two persons
2, "one another" is sued among the persons or more
3, however, "each other" can be used between each two persons in a group

I also hear that lately the distinction above is not strictly observed and "each other" and "one another" are often used interchangeably.

I would like to know the current fact about this.
Please write some examples too, if it's ok.

Thank you in advance.

 

[KEN JPN]

My question has been self-resolved.

Grammar Girl : "Each Other" Versus "One Another" :: Quick and Dirty Tips ™

In the above URL, I learned the historical background, where the distinction people often believe comes from, what was the fact, etc.