pkg go/ast, type IndexListExpr struct, X Expr
pkg go/ast, type TypeSpec struct, TypeParams *FieldList
pkg go/constant, method (Kind) String() string
pkg go/token, const TILDE = 88
pkg go/token, const TILDE Token
pkg go/types, func Instantiate(*Context, Type, []Type, bool) (Type, error)
pkg go/types, func NewContext() *Context
pkg go/types, func NewSignature //deprecated

		case *types.Union:
			var buf bytes.Buffer
			nu := emb.Len()
			for i := 0; i < nu; i++ {
				if i > 0 {
					buf.WriteString(" | ")
				}
				term := emb.Term(i)
				if term.Tilde() {
					buf.WriteByte('~')
				}
				w.writeType(&buf, term.Type())
			}
			list = append(list, buf.String())
		}
	}
	sort.Strings(list)
	return list
}

	<code>core(C)</code> and <code>A</code> must unify loosely.
	If <code>P</code> does not have a known type argument
	and <code>C</code> contains exactly one type term <code>T</code>
	that is not an underlying (tilde) type, unification adds the
	mapping <code>P ➞ T</code> to the map.
</li>
<li>
	If <code>C</code> does not have a core type
	and <code>P</code> has a known type argument <code>A</code>,