\version "2.12.2"

qBeam = {
	#(override-auto-beam-setting '(end 1 8 * *) 1 4 'Staff)
	#(override-auto-beam-setting '(end 1 8 * *) 2 4 'Staff)
}

rBeam = {
	#(revert-auto-beam-setting '(end 1 8 * *) 1 4 'Staff)
	#(revert-auto-beam-setting '(end 1 8 * *) 2 4 'Staff)
}

treble = \relative c {
	b''2 a4
}

middle = \relative c {
	\qBeam 
	\once \override Stem #'direction = #UP a8 g' e' c ~ c e
}

bass = \relative c {
	a2.
}

\score {
	\context Staff = guitar {
		\clef "treble_8"
		\key e \minor
		\time 3/4
		\mergeDifferentlyHeadedOn
		\mergeDifferentlyDottedOn
		<<
			\context Voice = "1" { \voiceOne \treble }
			\context Voice = "2" { \voiceTwo \middle }
			\context Voice = "4" { \voiceFour \bass }
		>>
	}
	\layout { }
}

\score {
	\context Staff = guitar {
		\clef "treble_8"
		\key e \minor
		\time 3/4
		\mergeDifferentlyHeadedOn
		\mergeDifferentlyDottedOn
		<<
%			\context Voice = "1" { \voiceOne \treble }
			\context Voice = "2" { \voiceTwo \middle }
			\context Voice = "4" { \voiceFour \bass }
		>>
	}
	\layout { }
}