MetaPost question

Hello,
I have attached a mpost program that provides for me a problem.
The visual result is a complete graph on 6 nodes.   There are
six "external" edges as well as 15 "internal" edges.
All the internal edges contain a number displayed twice.   However
when initially writing the program, I used the assignment  :=
on the second occurance.    But the MetaPost processor doesn't
accept this.    But I notice the  ppp  path is updated 5 times with
this approach.

I have attached the MetaPost program  sixSLP.mp,  a short TeX
program   sixSLP.tex as well as the visual output  sixSLP.pdf.

Comments would be greatly appreciated.

Walt Burkhard