User blog comment:Maxywaxy/how do five argument beaf arrays work/@comment-30754445-20181122155711/@comment-30754445-20181129112122

There seems to be a mistake in your expansion... but your general conclusion is correct.

In fact, it is impossible to fully reduce even {a,3,2,2} into 3-entry arrays.

Let's try expanding {3,3,2,2}:

{3,3,2,2} = {3, {3,2,2,2} ,1,2} = {3, {3,3,1,2} ,1,2} = {3, {3,3,{3,3,3}} ,1,2} = {3, {3,3,3↑↑↑3} ,1,2} = ...

And at this point we're pretty much screwed. The number of steps required to fully reduce this last expression into 3-entry arrays is about {3,3,3↑↑↑3} (give or take a couple of steps). That's:

3 [a (power tower of 7625597484987 threes) arrows] 3 steps.

And the resulting expression will be a comparable number of characters long.