[tryton] Problem with pyson, domain, and xml

[Francisco Maria Moyano Casco]

Greetings.
              Hello. I'm having a little issue with these sentences
             
                 <record model="ir.action.act_window.domain" 
id="act_maintenance_historical_request_state">
                       <field name="name">Today</field>
                      <field name="sequence" eval="10"/>
                      <field name="domain">[('state', 
'=','request'),('request_date',<=',DateTime(hour=0, minute=0, second=0, 
microsecond=0, delta_days=1))]</field>
                     <field name="act_window" ref="act_request"/>
                </record>

The server gives me this
             xml.sax._exceptions.SAXParseException: <unknown>:66:45: not 
well-formed (invalid token)

And the error is  on this operator (the one in bold)

<field name="domain">[('state', 
'=','request'),('request_date',*'<='*,DateTime(hour=0, 
minute=0, second=0, microsecond=0, delta_days=1))]</field>

Thanks.
        Francisco