impenetrable vs without a solution

impenetrable

noun

  • A person not openly given to friendship. 

adj

  • Opaque; obscure; not translucent or transparent. 

  • Not penetrable. 

  • Incomprehensible; fathomless; inscrutable. 

without a solution

How often have the words impenetrable and without a solution occurred in a corpus of books? (source: Google Ngram Viewer )