User blog comment:PsiCubed2/My attempt for creating an ψ(ψᵢ(0))-level notation for ordinals/@comment-39162-20170404170110

Something that I've wondered for a while is what does \psi_\kappa \left( n \right) represent? Is there anywhere where I can see that notation (specifically in the context where \psi_I \left( 1 \right) is the first omega fixed point) defined with some examples?