MODULE ::= EXPR*
EXPR ::=
| IN
| ASSERT
ASSERT ::= (assert_eq|assert_ne) tuple
IN ::= OR (in OR)?
OR ::= AND (or AND)*
AND ::= TERM (and TERM)*
TERM ::= FACTOR ((add|sub) FACTOR)*
FACTOR ::= USUB ((mul|div|mod) USUB)*
USUB ::= sub* NOT
NOT ::= not* POW
POW ::= LITERAL (pow LITERAL)?
LITERAL ::= 
| BUILTIN 
| TUPLE
| INDEX
| opar EXPR cpar
INDEX ::= 
| TUPLE osquare (EXPR (comma EXPR)*)? csquare
TUPLE ::=
| opar EXPR+ cpar
BUILTIN ::= num | bool