I am reading about the Kontsevich integral, following this text : https://pdfs.semanticscholar.org/635b/c6370e8aba381724eaaa36abefba7f7a5bec.pdf
At some point (page 10 to be exact) the author claims that if you have two composable tangles $T_1$ and $T_2$ then we have $$ Z(T_1 \bullet T_2) = Z(T_1) Z(T_2)$$ where for a tangle $T$, $Z(T)$ denotes its Kontsevich integral.
This may be a somewhat stupid question but for some reason I can not see the reason why.
