http://www.congreso.es/consti/constitucion/indice/titulos/articulos.jsp?ini=155&tipo=2
https://www.socialeurope.eu/2017/06/the-case-for-an-investment-state/
https://theconversation.com/ampliacion-o-profundizacion-de-la-union-europea-227125
https://ec.europa.eu/taxation_customs/business/company-tax/common-consolidated-corporate-tax-base-ccctb_en