diff --git a/Tupfile b/Tupfile
index eb5222b..76c3d4d 100644
--- a/Tupfile
+++ b/Tupfile
@@ -17,5 +17,5 @@ COMMON_SRCS = backtrace.cc common.cc sequence.cc
 PROGS = traverse_comp greedy_mds mdss2dot comp2rankdot
 PROGS += fms2mds optimize_rem_path_len mykkeltveit_set find_longest_path
 PROGS += champarnaud_set sketch_components syncmer_set syncmer_sketch frac_set
-PROGS += create_seed sketch_histo old_champarnaud_set
+PROGS += create_seed sketch_histo old_champarnaud_set opt_canon
 run ./rules.sh $(PROGS)
diff --git a/opt_canon.cc b/opt_canon.cc
new file mode 100644
index 0000000..8320d00
--- /dev/null
+++ b/opt_canon.cc
@@ -0,0 +1,83 @@
+#include <iostream>
+#include <unordered_set>
+
+#include "misc.hpp"
+#include "common.hpp"
+#include "tarjan_scc.hpp"
+
+#include "opt_canon.hpp"
+
+#ifndef K
+    #error Must define k-mer length K
+#endif
+
+#ifndef ALPHA
+    #error Must define alphabet length ALPHA
+#endif
+
+#include "mer_op.hpp"
+
+typedef mer_op_type<K, ALPHA> mer_ops;
+typedef mer_ops::mer_t mer_t;
+
+
+struct is_in_set {
+	const std::unordered_set<mer_t>& set;
+	is_in_set(const std::unordered_set<mer_t>& s) : set(s) {}
+	bool operator()(mer_t m) const { return set.find(m) != set.cend(); }
+};
+
+struct can_is_in_set {
+	const std::unordered_set<mer_t>& set;
+	can_is_in_set(const std::unordered_set<mer_t>& s) : set(s) {}
+	bool operator()(mer_t m) const { return set.find(mer_ops::canonical(m)) != set.cend(); }
+};
+
+struct is_in_union {
+	const std::unordered_set<mer_t>& set;
+	is_in_union(const std::unordered_set<mer_t>& s) : set(s) {}
+	bool operator()(mer_t m) const { return set.find(m) != set.cend() || set.find(mer_ops::reverse_comp(m)) != set.cend(); }
+};
+
+struct is_in_opt {
+	const std::unordered_set<mer_t>& set1;
+	const std::unordered_set<mer_t>& set2;
+	is_in_opt(const std::unordered_set<mer_t>& s1, const std::unordered_set<mer_t>& s2)
+		: set1(s1)
+		, set2(s2)
+		{}
+	bool operator()(mer_t m) const {
+		return (set1.find(m) != set1.cend() || set1.find(mer_ops::reverse_comp(m)) != set1.cend()) && \
+			(set2.find(m) == set2.end());
+	}
+};
+
+int main(int argc, char* argv[]) {
+	opt_canon args(argc, argv);
+	const auto mer_set = get_mds<std::unordered_set<mer_t>>(args.sketch_file_arg, args.sketch_arg);
+
+	tarjan_scc<mer_ops> comp_scc;
+	const is_in_set set_fn(mer_set);
+	const can_is_in_set can_fn(mer_set);
+	const auto counts_orig = comp_scc.scc_counts(set_fn);
+	std::cout << counts_orig.first << ' ' << counts_orig.second << '\n';
+
+	std::unordered_set<mer_t> remove;
+
+	// Greedily create the remove set. Should compare the SCCs themselves, not
+	// just their number and size. Sufficient for now....
+	for(const auto m : mer_set) {
+		if(can_fn(m)) continue; // Must be a super-set of canonical
+		// Try adding m to remove. If increase SCCs, don't keep it
+		remove.insert(m);
+		const is_in_opt opt(mer_set, remove);
+		const auto counts = comp_scc.scc_counts(opt);
+		if(counts.first > counts_orig.first || counts.second > counts_orig.second)
+			remove.erase(m);
+	}
+
+	std::cout << "orig   " << mer_set.size() << ": " << joinT<size_t>(mer_set, ',') << '\n';
+	std::cout << "remove " << remove.size() << ": " << joinT<size_t>(remove, ',') << '\n';
+
+	return EXIT_SUCCESS;
+}
diff --git a/opt_canon.yaggo b/opt_canon.yaggo
new file mode 100644
index 0000000..28134b0
--- /dev/null
+++ b/opt_canon.yaggo
@@ -0,0 +1,11 @@
+purpose "Find set one less than union"
+
+option('f', 'sketch-file') {
+  description 'File with sketch mer set'
+  c_string; typestr 'path'
+}
+
+arg('sketch') {
+  description 'k-mers'
+  c_string; multiple
+}
diff --git a/tarjan_scc.hpp b/tarjan_scc.hpp
index 68ffcc4..b4c015d 100644
--- a/tarjan_scc.hpp
+++ b/tarjan_scc.hpp
@@ -53,13 +53,17 @@ struct tarjan_scc {
 	}
 
 	template<typename Fn, typename E3>
-	std::pair<mer_t, mer_t> scc_counts(Fn fn, E3 new_visit = noprogress) {
+	std::pair<mer_t, mer_t> scc_counts(Fn fn, E3 new_visit) {
 		mer_t nb_scc = 0, nb_mers = 0;
 		auto new_scc = [&nb_scc](mer_t index) { ++nb_scc; };
 		auto new_mer = [&nb_mers](mer_t m) { ++nb_mers; };
 		scc_iterate(fn, new_scc, new_mer, new_visit);
 		return std::make_pair(nb_scc, nb_mers);
 	}
+	template<typename Fn>
+	inline std::pair<mer_t, mer_t> scc_counts(Fn fn) {
+		return scc_counts(fn, noprogress);
+	}
 
 	template<typename Fn, typename E3>
 	std::pair<mer_t, mer_t> scc_append(Fn fn, std::vector<mer_t>& mers, E3 new_visit = noprogress) {