Solution
= Solution
The <fundamental theorem of regular space curves> states that smooth functions $k>0$ and $\tau$ on an interval determine a smooth arc-length-parametrized curve in $\mathbb R^3$, unique up to a proper Euclidean motion. Consequently two such curves $\alpha$ and $\widetilde\alpha$ are related parameterwise by a proper Euclidean motion if and only if
$$
k(s)=\widetilde k(s),
\qquad
\tau(s)=\widetilde\tau(s)
$$
for every $s$.