text: **Reasoning and problem-solving**
  
  Early researchers developed algorithms that imitated step-by-step reasoning that humans use when they 
  solve puzzles or make logical deductions.[13] By the late 1980s and 1990s, methods were developed for 
  information, employing concepts from probability and 
  dealing with uncertain or 
  economics.[14] 
  
  incomplete 
  
  Many of these algorithms are insufficient for solving large reasoning problems because they experience a 
  "combinatorial explosion": They become exponentially slower as the problems grow.[15] Even humans 
  rarely use the step-by-step deduction that early AI research could model. They solve most of their 
  problems using fast, intuitive judgments.[16] Accurate and efficient reasoning is an unsolved problem. 