The rules that use the category "<number-sing>" are:

<width>

<number-sing> <distance_unit-sing>

<discourse_det-not_wh-sing>

<number-sing>

<discourse_det-sing>

<number-sing>

<discourse_det-not_wh_or_gq_or_dummy-sing>

<number-sing>

<discourse_det-indef-sing>

<number-sing>