# Difference between revisions of "Extended arrow notation"

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Extended arrow notation is a notation that was invented by Googology Wikia User Googleaarex: [1].

# Basic Notation

Basic Notation is very simple. It generalizes the normal arrow notation.

$$a \uparrow_2 b = a \underbrace{\uparrow\uparrow\dots\uparrow}_b a$$

$$a \uparrow_3 b = a \underbrace{\uparrow_2\uparrow_2\dots\uparrow_2}_b a$$

$$a \uparrow_n b = a \underbrace{\uparrow_{n-1}\uparrow_{n-1}\dots\uparrow_{n-1}}_b a$$

Note that all parts of Extended arrow notation, like Knuth's up-arrow notation, have expressions that are evaluated from the right.

Limit in FGH: $$f_\omega(n)$$

# Nested up-arrow notation

To extend the notation here, we first have to make a change: $$\uparrow_n = \uparrow_{\underbrace{\uparrow\uparrow\dots\uparrow}_{n-1}}$$

Then we turn the problem into Basic notation: $$a \uparrow_{\uparrow_2} b = a \uparrow_{\underbrace{\uparrow\uparrow\dots\uparrow}_b} a = a \uparrow_{b+1} b$$, and $$a \uparrow_{\uparrow\uparrow_2} b = a \underbrace{\uparrow_{\uparrow_2}\uparrow_{\uparrow_2}\dots\uparrow_{\uparrow_2}}_b a$$

Then: $$a \uparrow_{\uparrow_{\uparrow_2}} b = a \uparrow_{\uparrow_{b+1}} a$$ and so on.

Limit: $$\varepsilon_0$$

# Array up-arrow notation

Limit: $$\psi(\psi_{I(\omega, 0)}(0))$$