def retract(self, e, a, v):
    """ redact the value of an attribute
    """
    ta = datetime.datetime.now()
    ret = u"[:db/retract %i :%s %s]" % (e, a, dump_edn_val(v))
    rs = self.tx(ret)
    tb = datetime.datetime.now() - ta
    print cl('<<< retracted %s,%s,%s in %sms' % (e,a,v, tb.microseconds/1000.0), 'cyan')
    return rs