Algebra is an Arabic word meaning ‘to reunite sundered parts’. Omar Khayyám (1048-131), the Persian polymath and author of the Rubáiyát – made famous in English through Edward Fitzgerald’s version – was also a virtuoso mathematician. He solved various cases of the cubic equation, one of the greatest advances in algebra. In its symbolic representation of numbers and quantities in formulae and equations, restoring what is missing, it achieves its end with poetic elegance. In the eighteenth century, someone with a broken bone would seek a doctor who would perform ‘an algebra’ by setting it to ensure the fracture healed, the sundered reunited. Analogically, this is so often what poetry tries to do, attempting to reconcile so many disparate things.