The first three lines of Parting from the Four Attachments have this structure:
a ཞེན་ན b
If you are attached to a then b. However the b phrase in this case actually has the structure: c not which we interpret as not c. Therefore the whole structure of the first three lines becomes if you are attached to a then you do not have c.
This if/then structure is created by verb ན
The syntactic rules for this are:
S := a ཞེན་ན b
b := c not/without