'Build a list of RTEPairs from a RTE corpus.
:param fileids: a list of RTE corpus fileids
:type: list
:rtype: list(RTEPair)'

def pairs(self, fileids):

    if isinstance(fileids, string_types):
        fileids = [fileids]
    return concat([self._read_etree(self.xml(fileid)) for fileid in fileids])
