protected function processObsoleteLemmas($family, array $old_lemmas = [], array $new_lemmas = [])
    {
        // Get obsolete lemmas
        $lemmas = array_diff_key($old_lemmas, $new_lemmas);

        // Process all of the obsolete lemmas
        if (count($lemmas) > 0) {
            // Sort lemmas by key
            ksort($lemmas);

            // Remove all dynamic fields
            foreach ($lemmas as $key => $value) {
                $id = $this->decodeKey($key);

                // Remove any keys that can never be obsolete
                if ($this->neverObsolete($id)) {
                    Arr::set($this->final_lemmas,
                        $key, str_replace('%LEMMA', $value, $this->option('new-value'))
                    );

                    unset($lemmas[$key]);
                }
            }
        }

        // Check for obsolete lemmas
        if (count($lemmas) > 0) {
            $this->is_dirty = true;

            $this->comment("    " . count($lemmas) . " obsolete strings (will be deleted)");

            if ($this->option('verbose')) {
                foreach ($lemmas as $key => $value) {
                    $this->line("            <comment>" . $this->decodeKey($key) . "</comment>");
                }
            }
        }
    }