\ Begin {definition}
A \ textbf {parametric curve) is a continuous map $ c: I \ rightarrow X $, where $ X $ is a topological space. Let $ (X, d) $ be a metric space. Then we define
\ Begin {equation *} \ label {key}
L (c) = \ sup \ left \ {\ sum_ {i = 1} ^ {h} d \ left (c_t_ {i-1} Leq \ cdots \ leq t_k \ in I \ right \}.
\ End {equation *}
As the length of $ c $ with respect to the parameterization $ h $.
\ End {Definition}
If $ h $ is reduced, the length $ L (c) $ can not be reduced. A curve is called re-definable if $ L (c) <\ infty $. A curve can also be re-parameterized: $ \ varphi: I …