In mathematics, a uniqueness theorem is a theorem proving that certain conditions determine a unique solution. Examples of uniqueness theorems include:
Dear Behrad, there are not general existence and uniqueness theorems for nonlinear PDE problems; usually, if there is a global (= on all the PDE domain) E-U theorem for linear case, there is a local E-U theorem for nonlinear case (Signorini methods of sequential approximations).