<Tr> <Td> quotation marks </Td> <Td>' ' ""' ' "" </Td> </Tr> <Tr> <Td> semicolon </Td> <Td>; </Td> </Tr> <Tr> <Td> slash, stroke, solidus </Td> <Td> / ⁄ </Td> </Tr> <Tr> <Td_colspan="2"> <Table> <Tr> <Th_colspan="2"> Word dividers </Th> </Tr> <Tr> <Td> interpunct </Td> <Td> </Td> </Tr> <Tr> <Td> space </Td> <Td> </Td> </Tr> </Table> </Td> </Tr>

What does double vertical lines mean in math