Abbreviation: EucDom
A \emph{Euclidean domain} is an integral domains $\langle D,+,-,0,\cdot,1\rangle$ together with a function $d:D\setminus\{0\} \to\mathbf{N}$ such that
$\forall a,b\ (a\ne 0$, $b\neq 0 \Longrightarrow d(a)\le d(ab))$
$\forall a,b \exists q,r\ (a=b\cdot q+r$, $(r=0 \mbox{or} d(r)<d(b)))$
Example 1: $\langle\mathbb{Z},+,-,0,\cdot,1,d\rangle$, the ring of integers with addition, subtraction, zero, and multiplication is a Euclidean domain with $d(a)=|a|$.
$\begin{array}{lr}
f(1)= &1
f(2)= &1
f(3)= &1
f(4)= &1
f(5)= &1
f(6)= &0
\end{array}$