public ExternalSheet getExternalSheet(String firstSheetName, String lastSheetName, int externalWorkbookNumber) {throw new IllegalStateException("XSSF-style external references are not supported for HSSF");}

public ExternalSheet GetExternalSheet(String firstSheetName, string lastSheetName, int externalWorkbookNumber){throw new InvalidOperationException("XSSF-style external references are not supported for HSSF");}
