1 

     2 assert(syard(split("3 + 4 * ( 2 - 1 )")) == List("3", "4", "2", "1", "-", "*", "+"))

     3 assert(syard(split("( ( ( 3 ) ) + ( ( 4 + ( 5 ) ) ) )")) == List("3", "4", "5", "+", "+"))

     4 assert(syard(split("5 + 7 / 2")) == List("5", "7", "2", "/", "+"))

     5 assert(syard(split("5 * 7 / 2")) == List("5", "7", "*", "2", "/"))