Winding_shifting tangents

Hi all 

I’m trying to solve a definition for winding that redraws a path connecting shifted tangents at every vertices of the original poly line. I’m having problems at some vertices (see jpg. points 1 and 2). My first guess is that there’s a Boolean relation between angle of arrival and departure form that vertices that could solve the problem. I try to do it but I got complete stuck connecting the tangents definition with the Boolean relation.

Hopefully someone can help me with this.

Thanks !!!

MC