public string GetDebtsSummary(SettlementPlan plan)
        {
            StringBuilder builder = new StringBuilder();
            var           list    = plan.CalculateDebts();

            foreach (var d in list)
            {
                var p1 = ParticipantRepo.GetParticipant(d.PersonWhoOwes);
                var p2 = ParticipantRepo.GetParticipant(d.PersonWhoGetPayed);
                builder.AppendFormat("{0} needs to pay {1} {2} dollars\n", p1.DisplayName, p2.DisplayName, d.DebtAmount);
            }
            return(builder.ToString());
        }