The rules that use the vocabulary item "four" are:

<digit_one_to_five>

four

<digit-pl>

four

<hour>

four

oh four

zero four

one four

<digit_not_one>

four

<digit-not_9>

four

<digit_zero_to_five>

four

<ship_name>

lcac twenty four

lcac two four

lcu one six six four

lcu sixteen sixty four

<digit_zero_to_seven>

four

<digit-not_zero>

four

<digit>

four

<digit-not_zero-pl>

four

<digit-not_8_or_9>

four

<digit_one_to_four>

four

<up_to_six>

four

<digit-not_6_or_7_or_8_or_9>

four

<digit-not_0>

four

<digit_one_to_eight>

four

<digit-not_0_or_1_or_2>

four