Gregorian chant

Gregorian chant is often coded using four line staffs (see section [*]) and using special notes (called neumes) which are described in section [*]. But the gregorian chant also needs a special alto clef which is in fact the ancester of the modern alto clef. The gregorian alto clef can be invoked instead of the modern one by re-declaring the normalshapemediumseriesnormalshapemediumseries\clefdutr macro. Thus 

\def\clefdutiv{\gclefdut}
will cause the instrument number 4 (i.e. iv) to exhibit a gregorian C clef whenever the value of \cleftoskiv refers to an alto clef. The modern alto clef can be restored for that instrument by : 

\def\clefdutiv{\clefdutsymbol}