Command: prepend
  
Syntax: 
  s2 = prepend(s1, x)
  
Description: 
  Prepend x to the start of sequence s1. The length of s2 will be 
  length(s1) + 1. 
  
Comments: 
  If x is an atom this is the same as s2 = x & s1. If x is a 
  sequence it is definitely not the same. e.g.
  
  prepend({1,2,3}, {0,0})    
  -- {{0,0}, 1, 2, 3}
  
  {0,0} & {1,2,3}    
  -- {0, 0, 1, 2, 3}
  
  The case where s1 and s2 are the same variable is handled
  very efficiently.
  
Example: 
     s = {}
       for i = 1 to 10 do
   s = prepend(s, i)
        end for
        -- s is {10,9,8,7,6,5,4,3,2,1}
        
See Also: 
  append, concatenation (&) and sequence-formation {,,} operators 
  in refman.doc
  
