\score { \new ChoirStaff << \score_pre \transpose c \pitch_a \new Staff << \Ma \bars >> \lyricsto Va \La \transpose c \pitch_b \new Staff \Mb \lyricsto Vb \Lb \transpose c \pitch_c \new Staff \Mc \lyricsto Vc \Lc >> \layout { \context { \Voice \consists "Ambitus_engraver" keySignature = #'() } } }