colliding accidentals

[Orm Finnendahl]

Hi,

 where can I find documentation on how to avoid the collions of the
accidentals in the following example?

\version "2.10.0"

\score {
        \new Staff {
            \relative c' {
                <aeh! a!>8 
                << {aeh!8}\\{ a!8}>> 
            }
        }
        \layout {
            ragged-right = ##t
        }
    }

--
Orm