problem with slur across voices

[Tao Cumplido]

hello all,

I have a problem with slurring across voices in the following snippet.
the output is actually exactly what I want but I get lots of warnings when 
compiling, so I was wondering if anyone can come up with a better solution.
when I had the slur attached to the lower voice it collided with the stem of 
the upper voice.

Tao



\version "2.11.32"

hide = { \hideNotes \stemDown }

show = { \unHideNotes \stemUp }

\layout { ragged-right = ##t }

\relative c'
{
        \clef F
        \key es \minor
        << { bes4*3/4( \hide f16) \show es'4*3/4( \hide f,16)
        \show bes4*3/4( \hide f16) \show es'4*3/4( \hide f,16) \show } \\
        { bes16 f es f es' f, es f bes f es f es' f, es f } >> |
}
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