Try this:
If IsNull({u_case.cs_prev_chapter}) Then
{u_case.cs_type} = "bk" and {u_case.cs_date_filed} >= {?startdate} and {u_case.cs_date_filed} <= {?enddate}
Else
{u_case.cs_type} = "bk" and {u_case.cs_date_filed} >= {?startdate} and {u_case.cs_date_filed} <= {?enddate} and {u_case.cs_prev_chapter} in ["7","13"]
However, if you're using this in the Select Expert, please be aware that the use of the "If...Then...Else" construct means that Crystal will query for all of the data and do the filtering in memory instead of pushing the filter down to the database and having the database filter the data prior to returning it to Crystal. If you're data doesn't have many rows, this is not a big deal. However, if you're working with a fairly large data source, this can cause a report to be really slow. A better way to handle this in the Select Expert is to change the syntax to something like this:
((IsNull({u_case.cs_prev_chapter}) and
{u_case.cs_type} = "bk" and {u_case.cs_date_filed} >= {?startdate} and {u_case.cs_date_filed} <= {?enddate} )
OR
({u_case.cs_type} = "bk" and {u_case.cs_date_filed} >= {?startdate} and {u_case.cs_date_filed} <= {?enddate} and {u_case.cs_prev_chapter} in ["7", "13"]))
Note where I put the parentheses (bold, red) they MUST be included in order for this to work correctly!
-Dell