Function re_union 

pub fn re_union(r1: RegLan, r2: RegLan) -> RegLan

Union of two regular expressions

Example

use aws_smt_strings::smt_regular_expressions::*;

let r1 = re_star(str_to_re(&"a".into()));
let r2 = re_star(str_to_re(&"b".into()));
let u = re_union(r1, r2);
assert!(str_in_re(&"aaaa".into(), u));
assert!(str_in_re(&"bbb".into(), u));
assert!(str_in_re(&"".into(), u));