A list expression is defined by the following, in order:

i. An open bracket: [

ii. An operator

iii. An underscore: _

iv. An expression

v. An underscore: _

vi. An expression

vii. A close bracket: ]

A string in the JH-Lisp2 language is a single list expression. An example string in this language might be [add_[mod_4_3]_21]

Give a context-free grammar for JH-Lisp2