tie polyphony

[Gianmaria Lari]

Hello,

In the following code  

\version "2.19.80"

\fixed c' {

  r4 a b d'

  << {<e g c'>4 4 4 4} \\ c1 >>

}

... I would like to tie the "a" with the very first chord <e g c'>4. How I can do it?

Thank you, Gianmaria