Extending already inherited view?

Hey i am trying to extend the view which is already inherited

here is my product_form.py in party module

    <?xml version="1.0"?>
    <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
    this repository contains the full copyright notices and license terms. -->
    <data>
        <xpath expr="/form/field[@name='code']" position="replace">
            <group col="-1" name="code" string="">
                <field name="prefix_code"/>
                <field name="suffix_code"/>
            </group>
        </xpath>
        <xpath expr="/form/notebook/page[@id='general']/label[@name='type']"
            position="before">
            <label name="template"/>
            <field name="template" colspan="3"/>
        </xpath>
        <xpath expr="/form/notebook/page/field[@name='products']" position="replace">
            <group id="description" colspan="2" col="1" yexpand="1" yfill="1">
                <separator name="description"/>
                <field name="description"/>
            </group>
        </xpath>
        <xpath expr="/form/notebook/page[@id='general']" position="after">
            <page name="identifiers" col="1">
                <field name="identifiers" pre_validate="1"
                    view_ids="product.identifier_view_list_sequence"/>
            </page>
        </xpath>
    </data>

record xml of my custom module

    <record model="ir.ui.view" id="product_view_form">
            <field name="model">product.product</field>
            <field name="inherit" ref="product.product_view_form"/>
            <field name="name">product_form</field>
    </record>

product_form.xml in my custom module/view

    <?xml version="1.0"?>

    <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of

    this repository contains the full copyright notices and license terms. -->

        <data>
            <xpath expr="/xpath/page[@name='identifiers']" position="after">
                <field name="add_hsn"/>
            </xpath>
        </data>

but i am getting the following error

AttributeError: Couldn't find tag (xpath: /xpath/page[@name='identifiers']) in parent view!

if I’m not wrong, the correct path is:
/form/notebook/page[@name='identifiers']