backtracking vs progression

backtracking

noun
  • The act of one who, or that which, backtracks; a retracing of one's steps. 

  • The usage of a runway as a taxiway, especially at private strips and smaller airports. 

  • The act of building all possible solutions to a problem incrementally, abandoning any candidate solution if it cannot lead to a valid solution. 

progression

noun
  • The act of moving from one thing to another. 

  • A sequence obtained by adding or multiplying each term by a constant. 

  • chord progression 

  • The act of moving forward or proceeding in a course; motion onward. 

  • Development, increase, evolution. 

  • The making an exercise more exerting by manipulating the details of its performance like loaded weight, range of motion, angle, speed. 

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