Nesting Union Query in Join/Select

Hi I have set up my query as per below, I am stuck on where to put union query so I can filter it... code is ok until I add this.

[code]select distinct
a.PROP_NO,a.AMDT_SEQ,a.AMDT_SEQ_MAX_FLG,a.CTRT_EXP_DT,b.*,c.CTRT_SRC

from DMS_PRC_MN a
join (
    se...