... By Horace Horsnell The Lisbon Story (Hippodrome) LIBRETTISTS who seek to break away from hampering convention in their writing of -'books for musical plays need all the encouragement they can get. They are a kind of perpetual pioneers, faced with pitfalls and problems that might well daunt genius itself. Few are as fortunate-- or for that' matter as successful-- as Da Ponte, who adapted the ...