+ \relative c''
+ \new StaffGroup \with {
+ \remove "System_start_delimiter_engraver"
+ \override SpanBar #'glyph = #":"
+ } <<
+
+ %% solution 1
+ { c1 c1
+ <<
+ { c1 c1 }
+ \new Staff \with {
+ \remove "Time_signature_engraver"
+ } {
+ c,4^"ossia" es f fis g1
+ }
+ >>
+ c1 \break c c }