typedef struct pl_term_type
{ uintptr_t     magic;          /* PL_TYPE_MAGIC */
  char *        name;           /* name of the type */
  int           (*release)(pl_term a);
  int           (*compare)(pl_term a, pl_term b);
  int           (*pre_unify)(pl_term a, pl_term b);
  pl_term       (*deep_copy_term)(pl_term a, pl_term b);
  pl_term       (*copy_term)(pl_term a, pl_term b);
  int           (*post_unify)(pl_term a, pl_term b);
  int           (*write)(IOSTREAM *s, pl_term a, int flags);
  void          (*acquire)(pl_term a);
  ...
}

typedef struct pl_term
{ uintptr_t     magic;          /* PL_TERM_MAGIC */
  pl_term_type  type;          /* shared method mapping */
  pl_term_type  personal_overrides;
}