GNU LilyPond Notation Reference: 6.1.3 Paired substitution functions

### 6.1.3 Paired substitution functions

Some `\override` commands require a pair of numbers (called a `cons cell` in Scheme). To pass these numbers into a function, either use a `pair?` variable, or insert the `cons` into the music function.

> >     manualBeam =
> >     #(define-music-function (parser location beg-end)
> >                             (pair?)
> >     #{
> >       \once \override Beam #'positions = #$beg-end
> >     #})

> >     \relative {
> >       \manualBeam #'(3 . 6) c8 d e f
> >     }

or

>     manualBeam =
>     #(define-music-function (parser location beg end)
>                             (number? number?)
>     #{
>       \once \override Beam #'positions = #(cons $beg $end)
>     #})

>     \relative {
>       \manualBeam #3 #6 c8 d e f
>     }

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