Red lentils are about half the diameter of ordinary brown lentils. Do not substitute brown lentils, which will probably not cook fast enough. They often contain largish pebbles, so inspect them carefully. Rinse to get rid of dust, and drain. Red lentils are also very good by themselves, simply boiled with a few spices and served with butter.
Most sour cherries go into cherry syrups, pies, and preserves.
Canned sour cherries are quite good. You will usually find them in the home pie-making section of your market, near the canned blueberries and baker's supplies, or with the canned fruits. There are occasional stones. Middle Eastern stores will often have sour cherry preserves, which are too sweet for this recipe. Almost any stock or broth will work in this recipe.