You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: union_static.rs
    path of file: ./repos/rustfst/rustfst/src/algorithms/union
    
    the code of the file until where you have to start completion: use anyhow::Result;
use unsafe_unwrap::UnsafeUnwrap;

use crate::fst_properties::mutable_properties::union_properties;
use crate::fst_properties::FstProperties;
use crate::fst_traits::{AllocableFst, ExpandedFst, MutableFst};
use crate::semirings::Semiring;
use crate::tr::Tr;
use crate::{StateId, Trs, EPS_LABEL};

/// Performs the union of two wFSTs. If A
    
/// # fn main() -> Result<()> {
/// let mut fst_a : VectorFst<IntegerWeight> = fst![2 => 3];
/// let fst_b : VectorFst<IntegerWeight> = fst![6 => 5];
///
/// union(&mut fst_a, &fst_b)?;
/// let paths : HashSet<_> = fst_a.paths_iter().collect();
///
/// let mut paths_ref = HashSet::<FstPath<IntegerWeight>>::new();
/// paths_ref.insert(fst_path![2 => 3]);
/// paths_ref.insert(fst_path![6 => 5]);
///
/// assert_eq!(paths, paths_ref);
/// # Ok(())
/// # }