James Hilton (novelist) picked "Lost Horizon" as its first title in 1939. For that reason, the novel is frequently called the book that began the "paperback revolution." Hilton is said to have been inspired to write "Lost Horizon", and to invent "Shangri-La" by reading the "National Geographic Magazine" articles of Joseph Rock, an Austrian-American botanist and ethnologist exploring the southwestern Chinese provinces and Tibetan borderlands. Still living in Britain at the time, Hilton was perhaps influenced by the Tibetan travel articles of early travellers in Tibet whose writings were found in the British Library. Christian Zeeman, the Danish father of the mathematician Christopher
S-expression be formatted as pretty printed S-expressions using the function PPRINT (note: with two Ps, short for "pretty"-print). Lisp programs are valid s-expressions, but not all s-expressions are valid Lisp programs. codice_21 is a valid s-expression, but not a valid Lisp program, since Lisp uses prefix notation and a floating point number (here 1.0) is not valid as an operation (the first element of the expression). An S-expression preceded by a single quotation mark, as in codice_22, is syntactic sugar for a quoted S-expression, in this case codice_23. S-Expressions are often compared to XML, a key difference being that S-Expressions are