(setq a "first type")
"first type"
(setq b '(second TYPE))
(second TYPE)

`(a b c)
(a b c)
(backquote (a b c))
(a b c)

`(,a ,b c)
("first type" (second TYPE) c)
(backquote (,a ,b c))
(\,a \,b c)

`( , a , b c)
("first type" (second TYPE) c)
(backquote ( , a , b c))
"first type"

`( , @a , @b c)
Debugger entered--Lisp error: (void-variable @a)
(backquote ( , @a , @b c))
Debugger entered--Lisp error: (void-variable @a)

`( ,@a ,@b c)
(102 105 114 115 116 32 116 121 112 101 second TYPE c)
(backquote (,@a ,@b c))
(\,@a \,@b c)