https://www.otto-brenner-stiftung.de/fileadmin/user_data/stiftung/Aktuelles/AH93/AH_93_Haller_Web.pdf
http://www.europarl.europa.eu/sides/getDoc.do?pubRef=-%2F%2FEP%2F%2FNONSGML%2BCOMPARL%2BPE-602.995%2B01%2BDOC%2BPDF%2BV0%2F%2FEN
https://www.ifs.org.uk/uploads/Presentations/Carl%20Emmerson%2C%202017%20General%20Election%2C%20manifesto%20analysis.pdf