oblique mark vs sometimes

oblique mark

noun
  • Synonym of slash ⟨/⟩, sometimes (generally proscribed) inclusive of similar marks such as the backslash ⟨\⟩. 

sometimes

adv
  • On certain occasions, or in certain circumstances, but not always. 

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