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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_subgroupiteminsertion( cls, itemgroup, model, subgroup, indent) -> str: """Return a string defining the required types for the given combination of an exchange item group and a specific variable subgroup of an application model or class |Node|. Note that for `setitems` and `getitems` `setitemType` and `getitemType` are referenced, respectively, and for all others the model specific `mathitemType`: <element name="control" minOccurs="0" maxOccurs="unbounded"> <complexType> <sequence> <element ref="hpcb:selections" minOccurs="0"/> <element ref="hpcb:devices" minOccurs="0"/> <element name="area" type="hpcb:setitemType" minOccurs="0" maxOccurs="unbounded"/> <element name="nmbzones" </sequence> </complexType> </element> <element name="control" <element name="area" type="hpcb:getitemType" minOccurs="0" maxOccurs="unbounded"/> <element name="control" <element name="area" type="hpcb:hland_v1_mathitemType" minOccurs="0" maxOccurs="unbounded"/> For sequence classes, additional "series" elements are added: <element name="fluxes" <element name="tmean" type="hpcb:setitemType" minOccurs="0" maxOccurs="unbounded"/> <element name="tmean.series" type="hpcb:setitemType" minOccurs="0" maxOccurs="unbounded"/> <element name="tc" </sequence> </complexType> </element> """

        blanks1 = ' ' * (indent * 4)
        blanks2 = ' ' * ((indent+5) * 4 + 1)
        subs = [
            f'{blanks1}<element name="{subgroup.name}"',
            f'{blanks1}         minOccurs="0"',
            f'{blanks1}         maxOccurs="unbounded">',
            f'{blanks1}    <complexType>',
            f'{blanks1}        <sequence>',
            f'{blanks1}            <element ref="hpcb:selections"',
            f'{blanks1}                     minOccurs="0"/>',
            f'{blanks1}            <element ref="hpcb:devices"',
            f'{blanks1}                     minOccurs="0"/>']
        seriesflags = (False,) if subgroup.name == 'control' else (False, True)
        for variable in subgroup:
            for series in seriesflags:
                name = f'{variable.name}.series' if series else variable.name
                subs.append(f'{blanks1}            <element name="{name}"')
                if itemgroup == 'setitems':
                    subs.append(f'{blanks2}type="hpcb:setitemType"')
                elif itemgroup == 'getitems':
                    subs.append(f'{blanks2}type="hpcb:getitemType"')
                else:
                    subs.append(
                        f'{blanks2}type="hpcb:{model.name}_mathitemType"')
                subs.append(f'{blanks2}minOccurs="0"')
                subs.append(f'{blanks2}maxOccurs="unbounded"/>')
        subs.extend([
            f'{blanks1}        </sequence>',
            f'{blanks1}    </complexType>',
            f'{blanks1}</element>'])
        return '\n'.join(subs)