行政契約 單方變更權 契約必須遵守原則 公權力 公共服務之持續原則 公共服務之可變性原則 公權力(職權)不得讓渡原則 契約財務平衡原則 Administrative contract Power of unilateral modification Pacta sunt servanda Public authority The principle of continuity of public service The principle of variability of service public The principle of non-delegation of public authority The principle of financial equilibrium of contract