Jahama, SaidKfoury, A.J.2011-09-122011-09-121993-12-20Jahama, Said. "Type Reconstruction in the Presence of Polymorphic Recursion and Recursive Types", Technical Report BUCS-1993-019, Computer Science Department, Boston University, December 1993. [Available from: http://hdl.handle.net/2144/1477]https://hdl.handle.net/2144/1477We establish the equivalence of type reconstruction with polymorphic recursion and recursive types is equivalent to regular semi-unification which proves the undecidability of the corresponding type reconstruction problem. We also establish the equivalence of type reconstruction with polymorphic recursion and positive recursive types to a special case of regular semi-unification which we call positive regular semi-unification. The decidability of positive regular semi-unification is an open problem.en-USTechnical Report