rax_type_t rax_type_tuple_new_natural_cat(rax_type_t type_tuple_A,
 rax_type_t type_tuple_B);

Create a new tuple or set-of-tuple type by concatenating two tuple or set-of-tuple types, but leaving out duplicate fields (i.e. fields with the same label and type). Note that it works on any combination of tuple and set of tuple. Returns a set of tuple if one or both input types are a set of tuples.