Four Fours/Lemmata/Three Fours/81/Solutions/1

Puzzle: Three Fours: $81$

Using exactly $3$ instances of the number $4$, the task is to write an expression for $81$, using whatever arithmetical operations you consider necessary.

Solution

$81 = \paren {\dfrac 4 {. \dot 4} }^{\sqrt 4}$