Now, it is a well-ascertained and Undoubtable fact that the passion of love animates the bosoms of red men as well as white.
"The Prairie Chief"
R.M. Ballantyne
But she had never been so certain of her love,-of her love as a true, undoubted, and Undoubtable fact-of an unchangeable fact,-as she was now.
"An Old Man's Love"
Anthony Trollope
The prisoner's time, since he ceased to be a boy, has been employed in futile endeavours to satisfy the legal claims of this man; and I shall prove to you by most Undoubtable evidence that his industry in this object has been unceasing, and that his conduct as a son and a brother has been beyond all praise.
"The Macdermots of Ballycloran"
Anthony Trollope