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

<digit-pl>

six

<hour>

six

oh six

zero six

one six

<digit-5_or_6_or_7_or_8_or_9>

six

<digit_not_one>

six

<digit-not_9>

six

<ship_name>

lcu one six six five

lcu one six six four

lcu one six six three

<digit_zero_to_seven>

six

<digit-not_zero>

six

<digit>

six

<digit-not_zero-pl>

six

<digit-not_8_or_9>

six

<up_to_six>

six

<digit-not_0>

six

<digit_one_to_eight>

six

<digit-not_0_or_1_or_2>

six