The category "<nl_command-command>" can be expressed as follows:

<nl_command-command>

<basic_nl_command-command-gapsout_null-gapsin_null>

<basic_nl_command-command-gapsout_null-gapsin_null> <sequence_adv_nl_command>

<basic_nl_command-command-gapsout_null-gapsin_null> and <nl_command-command>