*  @param optag     The tag of the operation tree.
     *  @param env       The environment current at the operation.
     *  @param arg       The type of the operand.
     */
    Symbol resolveUnaryOperator(DiagnosticPosition pos, int optag, Env<AttrContext> env, Type arg) {
        return resolveOperator(pos, optag, env, List.of(arg));
    }