Four surgeons conducted their medical practices through a general partnership they owned, which obtained a $1.5 million loan from enterprise bank. the loan was secured by personal guarantees of the four doctors, each for $375,000. the partners have an agreement in writing that they will all equally liable for any debts of the partnership. two doctors then moved away. when the partnership failed to pay the remaining loan balance of $500,000, enterprise moved to enforce the personal guarantees by the two remaining doctors and won a judgment. those two doctors contended that they were only liable for one-quarter of the outstanding balance. who is liable for the judgment?