date_expression ::=
 {date_constant_name
 | date_function_call
 | date_literal
 | date_variable_name
 | :host_variable_name [:indicator_name]}
 [{+ | -} numeric_expression] [{+ | -} numeric_expression]]...

numeric_expression ::=
 numeric_subexpression 
 [{+ | - | * | /} numeric_subexpression] 
 [{+ | - | * | /} numeric_subexpression]...