ARMCHAIR TRAVEL FOR THE MIND: It was Sita Dulip who discovered, whilst stuck in an airport, unable to get anywhere, how to change planes - literally. With a kind of a twist and a slipping bend, easier to do than describe, she could go anywhere - be anywhere - because she was already between planes . . . and on the way back from her sister's wedding, she missed her plane in Chicago and found herself in Choom. The author, armed with this knowledge and Rornan's invaluable Handy Planetary Guide - although not the Encyclopedia Planeria, as that runs to forty-four volumes - has spent many happy years exploring places as diverse as Islac and the Veksian plane. CHANGING PLANES is an intriguing, enticing mixture of GULLIVER'S TRAVELS and THE HITCH HIKER'S GUIDE TO THE GALAXY; a cross between Dougla