Proposed extensions of the ML type system to incorporate global overloading include the systems of Kae88, CD091, Smi9l, Kae92, Jon92 and those related to the design of the functional programming language Haskell WaB89, CH092, niP93. These systems have in common the notion of a constrained type scheme which in some is realized by type kinds and in others as explicit predicates. An analysis of these type systems reveals that some are unsound with regard to a suitable criterion for typability and some adopt a notion of type generality that is inconsistent with that of system ML DaM82. Type systems, Global overloading.