use std::collections::{BTreeSet, HashMap};
fn f<'a>(a: &[&'a str]) -> Vec<Vec<&'a str>> { // '
	fn g(mut a: Vec<BTreeSet<usize>>) -> Vec<BTreeSet<usize>> {
		let comb = |n| (0..n).flat_map(move |i| (i + 1..n).map(move |j| (i, j)));
		match comb(a.len()).find(|&(i, j)| !a[i].is_disjoint(&a[j])) {
			None => a,
			Some((i, j)) => {
				let js = a.remove(j);
				a[i].extend(js);
				g(a)
			},
		}
	}
    let h = a.iter().map(|&s| s.split('=')).flatten().rev().enumerate().map(|(p, s)| (s, a.len() * 2 - p)).collect::<HashMap<_, _>>();
	let a = a.iter().map(|&s| s.split('=').flat_map(|k| h.get(k)).cloned().collect::<BTreeSet<_>>()).collect();
	let hi = h.iter().map(|(&k, &v)| (v, k)).collect::<HashMap<_, _>>();
	g(a).iter().map(|set| set.iter().flat_map(|i| hi.get(i)).cloned().collect()).collect()
}
fn main() {
    let v = ["a1=a2", "b1=b2", "b3=b2", "c1=c2", "e1=e2",
             "a3=a4", "c3=c4", "e1=e3", "a2=a4", "c3=c1",
             "b3=a4", "c2=d1", "a4=a5", "d2=c1", "b4=b3", "d3=c3"];
    println!("{:?}", f(&v));
}

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