 nor shall the Trustee be required to take notice of any default or `event of default' hereunder, and it may, for all purposes, conclusively assume that there has been no default or `event of default' hereunder, unless and until notified in writing thereof by the holders of at least twenty-five per centum in principal amount of the Prudence-Bonds issued hereunder and then outstanding, distinctly specifying such default, nor shall the Trustee take any action in respect to any default or `event of default' unless requested to take action in respect thereto by a writing signed by the holders of not less than twenty-five per centum in principal amount of the Prudence-Bonds issued hereunder and then outstanding, and upon being tendered indemnity as hereinbefore provided." 