 Consistent heuristic

In the study of path-finding problems in artificial intelligence, a heuristic function is said to be consistent, or monotone, if its estimate is always less than or equal to the estimated distance from any neighbouring vertex to the goal, plus the cost of reaching that neighbour.Formally, for every node "N" and each successor "P" of "N", the estimated cost of reaching the goal from "N" is no greater than the step cost of getting to "P" plus the estimated cost of reaching the goal from "P".