diff --git a/main.cpp b/main.cpp
index 0b0cdd5..9808f0c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -16,39 +16,66 @@ namespace po = boost::program_options;
 
 int main(int argc, char *argv[])
 {
-    std::string letters;
+    icu::UnicodeString letters;
+    icu::UnicodeString mustHaveLetters;
     int wordLengthMin{1};
     int wordLengthMax{1024};
     int lineLength{60};
     int numLines{4};
     std::string wordsFile{"/usr/share/dict/ngerman"};
     bool lowercase{false};
+    bool startsCapital{false};
 
     po::options_description desc("Erlaubte Optionen");
     desc.add_options()("help,h", "Ausgabe der Hilfe")(
-        "characters,c", po::value<std::string>(&letters), "Enthaltene Buchstaben")(
-        "min-length", po::value<int>(&wordLengthMin),
-        "Minimale Wortlänge")("max-length", po::value<int>(&wordLengthMax), "Maximale Wortlänge")(
-        "line-length", po::value<int>(&lineLength),
-        "Maximale Zeilenlänge")("num-lines,n", po::value<int>(&numLines), "Anzahl Zeilen")(
-        "lowercase", po::bool_switch(&lowercase), "Ausgabe nur klein geschrieben")(
-        "dictfile,d", po::value<std::string>(&wordsFile), "Pfad zur Wörterbuchdatei");
+        "characters,c", po::value<icu::UnicodeString>(&letters), "Erlaubte Buchstaben")(
+        "must-have,m", po::value<icu::UnicodeString>(&mustHaveLetters),
+        "Buchstaben, die im Wort vorhanden sein *müssen* (nur in Verbindung mit --characters; "
+        "Buchstaben müssen davon Subset sein.)")("min-length", po::value<int>(&wordLengthMin),
+                                                 "Minimale Wortlänge")(
+        "max-length", po::value<int>(&wordLengthMax),
+        "Maximale Wortlänge")("line-length", po::value<int>(&lineLength), "Maximale Zeilenlänge")(
+        "num-lines,n", po::value<int>(&numLines), "Anzahl Zeilen")(
+        "dictfile,d", po::value<std::string>(&wordsFile), "Pfad zur Wörterbuchdatei")(
+        "lowercase,l", po::bool_switch(&lowercase),
+        "Ausgabe nur klein geschrieben")("starts-capital,s", po::bool_switch(&startsCapital),
+                                         "Wort muss mit einem Großbuchstaben beginnen");
 
     po::variables_map vm;
-    po::store(po::parse_command_line(argc, argv, desc), vm);
-    po::notify(vm);
+    try {
+        po::store(po::parse_command_line(argc, argv, desc), vm);
+        po::notify(vm);
+    } catch (po::error &err) {
+        std::cerr << "Fehler beim Verarbeiten der Optionen:\n";
+        std::cerr << err.what() << std::endl;
+        return 1;
+    }
 
     if (vm.contains("help")) {
         std::cout << desc << std::endl;
         return 1;
     }
 
+    if (mustHaveLetters.length() > 0) {
+        for (int i{0}; i < mustHaveLetters.length(); i++) {
+            auto ch = mustHaveLetters.charAt(i);
+            if (letters.indexOf(ch) == -1) {
+                std::cout
+                    << "Die Buchstaben von --must-have müssen ein Subset von --characters sein."
+                    << std::endl;
+                return 1;
+            }
+        }
+    }
+
     std::ifstream infile(wordsFile);
     std::string line;
     icu::UnicodeString uline;
     std::vector<icu::UnicodeString> words;
-    icu::UnicodeString ucLetters = icu::UnicodeString::fromUTF8(letters);
-    icu::UnicodeString ucLettersUpper = icu::UnicodeString::fromUTF8(letters).toUpper();
+    icu::UnicodeString lettersUpper = letters;
+    lettersUpper.toUpper();
+    icu::UnicodeString mustHaveLettersUpper = mustHaveLetters;
+    mustHaveLettersUpper.toUpper();
     long counter{0};
 
     if (!std::filesystem::exists(wordsFile)) {
@@ -63,11 +90,30 @@ int main(int argc, char *argv[])
         if (length < wordLengthMin || length > wordLengthMax)
             continue;
 
-        if (ucLetters.length() > 0) {
+        if (mustHaveLetters.length() > 0) {
             bool valid = true;
-            for (int i{0}; i < uline.length(); i++) {
+            for (int i{0}; i < mustHaveLetters.length(); i++) {
+                auto ch = mustHaveLetters.charAt(i);
+                auto chU = mustHaveLettersUpper.charAt(i);
+                if (uline.indexOf(ch) == -1 && uline.indexOf(chU) == -1) {
+                    valid = false;
+                    break;
+                }
+            }
+            if (!valid)
+                continue;
+        }
+
+        if (letters.length() > 0) {
+            bool valid = true;
+            for (int i{0}; i < length; i++) {
                 auto ch = uline.charAt(i);
-                if (ucLetters.indexOf(ch) == -1 && ucLettersUpper.indexOf(ch) == -1) {
+                if (startsCapital && i == 0) {
+                    if (lettersUpper.indexOf(ch) == -1) {
+                        valid = false;
+                        break;
+                    }
+                } else if (letters.indexOf(ch) == -1 && lettersUpper.indexOf(ch) == -1) {
                     valid = false;
                     break;
                 }
@@ -83,11 +129,17 @@ int main(int argc, char *argv[])
         counter++;
     }
 
+    if (counter == 0) {
+        std::cout << "Keine Wörter mit den angegebenen Kriterien gefunden." << std::endl;
+        return 0;
+    }
+
     std::cout << "Anzahl infrage kommender Wörter: " << counter << "\n" << std::endl;
 
     std::random_device rdev;
     std::mt19937 rng(rdev());
     std::uniform_int_distribution<std::mt19937::result_type> distrib(0, words.size() - 1);
+
     for (int i{0}; i < numLines; i++) {
         icu::UnicodeString lectionLine;
         while (lectionLine.length() < lineLength) {