if xi != nil {
			// All xi methods must exist in y and corresponding signatures must unify.
			xmethods := xi.typeSet().methods
			for _, xm := range xmethods {
				obj, _, _ := LookupFieldOrMethod(y, false, xm.pkg, xm.name)
				if ym, _ := obj.(*Func); ym == nil || !u.nify(xm.typ, ym.typ, exact, p) {
					return false
				}
			}
			return true
		}
	}

		{"IsInterface", Func, 5},
		{"IsNumeric", Const, 5},
		{"IsOrdered", Const, 5},
		{"IsString", Const, 5},
		{"IsUnsigned", Const, 5},
		{"IsUntyped", Const, 5},
		{"Label", Type, 5},
		{"LookupFieldOrMethod", Func, 5},
		{"Map", Type, 5},
		{"MethodExpr", Const, 5},
		{"MethodSet", Type, 5},
		{"MethodVal", Const, 5},
		{"MissingMethod", Func, 5},
		{"Named", Type, 5},
		{"NewAlias", Func, 22},