; (x)
;; This is not valid syntax for anything. It could be a variable x, if only it stood alone and not inside parentheses.

; (+ 1 (not x))
  This is legal , I think . It is an expression that starts with a primitive expression , followed by a value , followed by another expression ( not x ) . The inner expression is valid since it conforms to ( primitive expr ) , and the outer expression has the valid format ( primitive expr expr ) , where the second expr is that inner expression .

; (+ 1 2 3)
;; This is legal, it matches the format (primitive expr expr expr), which is valid syntax for an expression, and each of its `expr`s is a valid expression that is just a value.

 (x)
 This is not valid syntax for anything. It could be a variable x, if only it stood alone and not inside parentheses.
 (+ 1 (not x))
 (+ 1 2 3)
 This is legal, it matches the format (primitive expr expr expr), which is valid syntax for an expression, and each of its `expr`s is a valid expression that is just a value.

  This is legal , I think . It is an expression that starts with a primitive expression , followed by a value , followed by another expression ( not x ) . The inner expression is valid since it conforms to ( primitive expr ) , and the outer expression has the valid format ( primitive expr expr ) , where the second expr is that inner expression .

