RECOVERING. NELSON MANDELA, 76, South African President; from surgery to remove a cataract from his left eye; in Johannesburg. The operation, though successful, was difficult enough to prompt surgeons to postpone a similar operation on Mandela's right eye because of a condition he developed while breaking rocks on Robben Island, where he was held for much of his 27 years' imprisonment: his tear glands were "burnt out" by the alkalinity in the limestone. Mandela should be back at work in about a week, wearing an eye patch.