Blank Symbol (Turing Machine)

computation

Definition

Blank Symbol ( Turing Machine)

The blank symbol, denoted by $B$ or $\square$, is a special symbol in the tape alphabet of a Turing machine that represents an empty cell. It is the only symbol allowed to appear on the tape infinitely many times, as almost all cells on the tape are initialised with the blank symbol.

The blank symbol is typically not part of the input alphabet $\Sigma$, but it is always part of the tape alphabet $\Gamma$($\Sigma \subset \Gamma$ and $B\in \Gamma \setminus \Sigma$).