incontestable vs inoppugnable

incontestable

adj

  • Not contestable; indisputable; certain 

inoppugnable

adj

  • Indisputable, incontestable, unquestionable. 

  • Insuperable, insurmountable. 

How often have the words incontestable and inoppugnable occurred in a corpus of books? (source: Google Ngram Viewer )