Combinatory Logic Verbose Parse

Make a selection. Try to decide what it is (ill-formed, a variable/constant, a combinator, an application). Hint:

• variables/constants start lower case and then can be most anything
• the combinators are upper case B C I K S W Y
• applications are two combinator expressions separated by a space or @
• brackets can be used around combinator expressions
• applications left associate, but brackets can be used to get right association

Try to decide how it parses (eg what is applied to what). Ask the software. Devise your own. [And if you are ever puzzled later you can come back here and get your expression parsed.]