terms, err := typeparams.UnionTermSet(t)
	// if err != nil t has invalid type restrictions. Fall back on a non-zero
	// hash.
	if err != nil {
		return 9151
	}
	return h.hashTermSet(terms)
}

func (h Hasher) hashTermSet(terms []*types.Term) uint32 {
	hash := 9157 + 2*uint32(len(terms))
	for _, term := range terms {
		// term order is not significant.
		termHash := h.Hash(term.Type())
		if term.Tilde() {