}
		w.typ(x)
		w.string(": ")
		w.typ(u.at(x))
	}
	w.byte(']')
	return buf.String()
}

type typeParamsById []*TypeParam

func (s typeParamsById) Len() int           { return len(s) }
func (s typeParamsById) Less(i, j int) bool { return s[i].id < s[j].id }
func (s typeParamsById) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

// join unifies the given type parameters x and y.

		}
		w.typ(x)
		w.string(": ")
		w.typ(u.at(x))
	}
	w.byte(']')
	return buf.String()
}

type typeParamsById []*TypeParam

func (s typeParamsById) Len() int           { return len(s) }
func (s typeParamsById) Less(i, j int) bool { return s[i].id < s[j].id }
func (s typeParamsById) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

// join unifies the given type parameters x and y.