User blog comment:SandstoneGem/Sandstone's second notation/@comment-30754445-20170610181026/@comment-32126147-20170610184258

[x] means x^10^x^10

so [4] means 4^10^4^10

or x|y means x^10^y!

so 2|3 means 2^10^3! where ! - factorial

got it? ;)