Mix the natural yoghurt, sour cream, cream and ketchup together well. Then cut the hard-boiled eggs into small pieces and fold in carefully. Open the tangerine can and mix some tangerine juice into the mixture. Fold the shrimp into the cream and season with curry, salt, pepper and a teaspoon of sugar. Finally the mandarins are added. Let the shrimp salad stand in the refrigerator for 2 hours.