Expansion refers to the function \(a \{\{1\}\} b = a \{a \{\cdots \{a\} \cdots\}a\}a\), where there are b a's from the center out.[1] It is \(\{a,b,1,2\}\) in BEAF and a{X+1}b in X-Sequence Hyper-Exponential Notation. The notation a{c}b means {a,b,c}, which is a "c + 2"-ated to b, using the bracket operator.
The function eventually dominates any hyper-operator, such as tetration, pentation or even centation.
Graham's number is defined using a very close variant of expansion. It is \(3 \{\{1\}\} 65\) with the central 3 replaced with a 4.
a{{1}}b is exactly equal to [a,a,a,b-1] in the Graham Array Notation.
By Bird's Proof, \(a \{\{1\}\} b > a \rightarrow a \rightarrow (b-1) \rightarrow 2\) using chained arrow notation.
Examples 
Edit
- \(2\ \{\{1\}\}\ 2\) = 4
- \(2\ \{\{1\}\}\ 3 = 2\{2\{2\}2\}2 = 2\{4\}2 = 2\{3\}2 = 2\{2\}2 = 2\{1\}2 = 4\)
- In fact, if the base is equal to 2 and prime is ≥ 2, then the result will always be 4.
- \(3\ \{\{1\}\}\ 2 = \{3,2,1,2\} = 3 \{3\} 3 = 3\uparrow\uparrow\uparrow 3\) (tritri)
- \(a\ \{\{1\}\}\ 2 = \{a,2,1,2\} = a \{a\} a = a\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{a}a\)
- \(3\ \{\{1\}\}\ 3 = \{3,3,1,2\} = 3 \{3 \{3\} 3\} 3 = 3\{\text{tritri}\}3 = 3\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{\text{tritri}}3\)
- \(4\ \{\{1\}\}\ 3 = \{4,3,1,2\} = 4 \{4 \{4\} 4 \}4 = 4 \{\)Template:Mathlink\(\} 4 = 4\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{\text{tritet}}4\)
- \(a\ \{\{1\}\}\ 3 = \{a,3,1,2\} = a \{a \{a\} a\} a = a\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{a\{a\}a}a\)
- \(3\ \{\{1\}\}\ 4 = \{3,4,1,2\} = 3 \{3 \{3 \{3\} 3\} 3 \}3 = 3 \{3 \{\text{tritri}\} 3\} 3 = 3\{\ \{3,3,1,2\}\ \}3 = 3\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{\{3,3,1,2\} }3\) = \(3 \uparrow^{3 \uparrow^{3 \uparrow^{3}3}3}3\)
- \(a\ \{\{1\}\}\ 4 = \{a,4,1,2\} = a \{a \{a \{a\} a\} a \}a = a\underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{a\{a\{a\}a\}a}a\)
- \(10 \{\{1\}\} 100 = \{10,100,1,2\} = \{10,10,\{10,99,1,2 \}\} = 10 \underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{\{10,99,1,2 \} }10\) (corporal)
- \(a \{\{1\}\} b = \{a,b,1,2\} = \{a,a,\{a,b-1,1,2 \}\} = a \underbrace{\uparrow\uparrow\cdots\uparrow\uparrow}_{\{a,b-1,1,2\} }a\)
Pseudocode Edit
Below is an example of pseudocode for expansion.
function expansion(a, b):
result := a
repeat b - 1 times:
result := hyper(a, a, result + 2)
return result
function hyper(a, b, n):
if n = 1:
return a + b
result := a
repeat b - 1 times:
result := hyper(a, result, n - 1)
return result
