private static void putCompoundGroup(String language, String... features) {
        String chain = "";
        for (String feature : features)
            chain += feature + featureSepChar;
        chain = chain.substring(0, chain.length() - 1); // remove trailing "^"
        Map<String, SortedSet<String>> sampaSymbols = sampaMappings.getSymbolsWithFeatures(language, features);
        for (String side : sampaSymbols.keySet()) {
            Boolean repeatedGroup = false;
            String repeatedSign = "";
            SortedSet<String> symbols = sampaSymbols.get(side);
            if (!symbols.isEmpty()) {
                if (groups.containsValue(symbols)) {
                    repeatedSign = "*";
                    repeatedGroup = true;
                }
                if ((repeatedGroup && outputRepeatedGroups) || !repeatedGroup)
                    groups.put(chain + side + repeatedSign, symbols);
            }
        }
    }