<Ul> <Li> Import </Li> <Li> Export </Li> </Ul> <Li> Free trade zone </Li> <Tr> <Td> Research (show) <Table> <Tr> <Th> Academic </Th> </Tr> <Tr> <Td> <Ul> <Li> Mihir A. Desai </Li> <Li> Dhammika Dharmapala </Li> <Li> James R. Hines Jr . </Li> <Li> Joel Slemrod </Li> <Li> Gabriel Zucman </Li> </Ul> </Td> </Tr> <Tr> <Th> Advocacy Groups </Th> </Tr> <Tr> <Td> <Ul> <Li> Tax Justice Network (TJN) </Li> <Li> Institute on Taxation and Economic Policy (ITEP) </Li> <Li> Oxfam (UK) </Li> <Li> Tax Foundation (US) </Li> <Li> Tax Policy Center (US) </Li> </Ul> </Td> </Tr> </Table> </Td> </Tr> <Table> <Tr> <Th> Academic </Th> </Tr> <Tr> <Td> <Ul> <Li> Mihir A. Desai </Li> <Li> Dhammika Dharmapala </Li> <Li> James R. Hines Jr . </Li> <Li> Joel Slemrod </Li> <Li> Gabriel Zucman </Li> </Ul> </Td> </Tr> <Tr> <Th> Advocacy Groups </Th> </Tr> <Tr> <Td> <Ul> <Li> Tax Justice Network (TJN) </Li> <Li> Institute on Taxation and Economic Policy (ITEP) </Li> <Li> Oxfam (UK) </Li> <Li> Tax Foundation (US) </Li> <Li> Tax Policy Center (US) </Li> </Ul> </Td> </Tr> </Table>

How many countries have a progressive tax system