= Instruction of a Turing machine
{title2=$\delta(q,a)=(p,b,D)$}
= Turing machine instruction
{c}
{synonym}
For a deterministic single-tape <Turing machine>, an instruction reads a state $q$ and scanned tape symbol $a$, writes $b$, changes state to $p$, and moves the head one cell left, one cell right, or not at all according to $D$. The state and tape alphabets are finite; an undefined transition halts. A dedicated terminal state can be introduced by directing undefined transitions to it without changing whether computation halts.
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