boolean_factor

boolean_factor 
      ::= 
      boolean_literal 
      | variable_name 
      | ( function [ "(" plsql_exp_list ")" ] ) 
      | ( "(" boolean_exp ")" ) 
      | ( plsql_expression 
      ( ( relational_op plsql_expression ) 
      | ( "is" [ "not" ] "null" ) 
      | ( [ "not" ] "like" match_string ) 
      | ( [ "not" ] "between" plsql_expression 
      "and" plsql_expression ) 
      | ( [ "not" ] "in" "(" plsql_exp_list ")" ) 
      | ( ( cursor_name | subquery ) 
      ( "%notfound" | "%found" | "%isopen" ) ) ) ) 

This rule is call by

-> boolean_term