```xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns4:query_definition xmlns:ns2="http://www.i2b2.org/xsd/cell/crc/psm/1.1/" xmlns:ns4="http://www.i2b2.org/xsd/cell/crc/psm/querydefinition/1.1/" xmlns:ns3="http://www.i2b2.org/xsd/cell/crc/psm/analysisdefinition/1.1/">
    <query_name>(t) DoseHypertensive di@11:13:50</query_name>
    <query_timing>ANY</query_timing>
    <specificity_scale>0</specificity_scale>
    <subquery_constraint>
        <first_query>
            <query_id>Observation A</query_id>
            <join_column>STARTDATE</join_column>
            <aggregate_operator>FIRST</aggregate_operator>
        </first_query>
        <operator>LESS</operator>
        <second_query>
            <query_id>Observation B</query_id>
            <join_column>STARTDATE</join_column>
            <aggregate_operator>FIRST</aggregate_operator>
        </second_query>
    </subquery_constraint>
    <subquery>
        <query_id>Observation A</query_id>
        <query_type>EVENT</query_type>
        <query_name>Observation A</query_name>
        <query_timing>SAMEINSTANCENUM</query_timing>
        <specificity_scale>0</specificity_scale>
        <panel>
            <panel_number>0</panel_number>
            <panel_timing>SAMEINSTANCENUM</panel_timing>
            <panel_accuracy_scale>100</panel_accuracy_scale>
            <invert>0</invert>
            <total_item_occurrences>1</total_item_occurrences>
            <item>
                <hlevel>5</hlevel>
                <item_name>Acebutolol</item_name>
                <item_key>\\i2b2_MEDS\i2b2\Medications\MUL\(LME68) cardiovascular agents\(LME77) beta-adrenergic blocking agents\(LME78) cardioselective beta blockers\acebutolol\</item_key>
                <item_icon>FA</item_icon>
                <tooltip>medications \ cardiovascular agents \ beta-adrenergic blocking agents \ cardioselective beta blockers \ acebutolol</tooltip>
                <class>ENC</class>
                <constrain_by_modifier>
                    <modifier_name>Dose</modifier_name>
                    <modifier_key>\\i2b2_MEDS\Medication\Dose\</modifier_key>
                    <applied_path>\i2b2\Medications\MUL\(LME68) cardiovascular agents\(LME77) beta-adrenergic blocking agents\(LME78) cardioselective beta blockers\acebutolol\%</applied_path>
                    <constrain_by_value>
                        <value_operator>LT</value_operator>
                        <value_constraint>1000</value_constraint>
                        <value_unit_of_measure>mg</value_unit_of_measure>
                        <value_type>NUMBER</value_type>
                    </constrain_by_value>
                </constrain_by_modifier>
                <item_is_synonym>false</item_is_synonym>
            </item>
        </panel>
    </subquery>
    <subquery>
        <query_id>Observation B</query_id>
        <query_type>EVENT</query_type>
        <query_name>Observation B</query_name>
        <query_timing>SAMEINSTANCENUM</query_timing>
        <specificity_scale>0</specificity_scale>
        <panel>
            <panel_number>0</panel_number>
            <panel_timing>SAMEINSTANCENUM</panel_timing>
            <panel_accuracy_scale>100</panel_accuracy_scale>
            <invert>0</invert>
            <total_item_occurrences>1</total_item_occurrences>
            <item>
                <hlevel>3</hlevel>
                <item_name>Hypertensive disease</item_name>
                <item_key>\\i2b2_DIAG\i2b2\Diagnoses\Circulatory system (390-459)\Hypertensive disease (401-405)\</item_key>
                <item_icon>FA</item_icon>
                <tooltip>Diagnoses \ Circulatory system \ Hypertensive disease</tooltip>
                <class>ENC</class>
                <item_is_synonym>false</item_is_synonym>
            </item>
        </panel>
    </subquery>
</ns4:query_definition>

```

I want to find all patients who have a first-time encounter with a diagnosis of hypertensive disease (ICD-9 codes 401-405) and were prescribed a dose of acebutolol (a beta-blocker medication) that is less than 1000 mg at the same instance number.