complex_constraint_err.m:016: In declaration for predicate `t'/1:
complex_constraint_err.m:016:   error in type class constraints: type variable
complex_constraint_err.m:016:   `C' occurs in the constraints, but is not
complex_constraint_err.m:016:   determined by the predicate's argument types.
complex_constraint_err.m:016:   All types occurring in typeclass constraints
complex_constraint_err.m:016:   must be fully determined. A type is fully
complex_constraint_err.m:016:   determined if one of the following holds:
complex_constraint_err.m:016:   1) All type variables occurring in the type are
complex_constraint_err.m:016:   determined.
complex_constraint_err.m:016:   2) The type occurs in a constraint argument,
complex_constraint_err.m:016:   that argument is in the range of some
complex_constraint_err.m:016:   functional dependency for that class, and the
complex_constraint_err.m:016:   types in all of the domain arguments for that
complex_constraint_err.m:016:   functional dependency are fully determined.
complex_constraint_err.m:016:   A type variable is determined if one of the
complex_constraint_err.m:016:   following holds:
complex_constraint_err.m:016:   1) The type variable occurs in the argument
complex_constraint_err.m:016:   types of the predicate, function, or
complex_constraint_err.m:016:   constructor which is constrained.
complex_constraint_err.m:016:   2) The type variable occurs in a type which is
complex_constraint_err.m:016:   fully determined.
complex_constraint_err.m:016:   See the "Functional dependencies" section of
complex_constraint_err.m:016:   the reference manual for details.
complex_constraint_err.m:020: In declaration for predicate `u'/1:
complex_constraint_err.m:020:   error in type class constraints: type variables
complex_constraint_err.m:020:   `Z' and `X' occur in the constraints, but are
complex_constraint_err.m:020:   not determined by the predicate's argument
complex_constraint_err.m:020:   types.