in src/main/java/org/jetbrains/jetCheck/Generator.java [151:159]
public static <T> Generator<T> frequency(int weight1, Generator<? extends T> alternative1,
int weight2, Generator<? extends T> alternative2,
int weight3, Generator<? extends T> alternative3) {
LinkedHashMap<Generator<? extends T>, Integer> map = new LinkedHashMap<>();
map.put(alternative1, weight1);
map.put(alternative2, weight2);
map.put(alternative3, weight3);
return frequency(map);
}