Climb from the start word at the top down to the GOAL waiting at the bottom of your board — change one letter at a time. Every rung must be a real word.
Changed A→O — one letter, still a real word. Green means that letter already matches the goal.
Par 4 Par is the fewest steps the puzzle can be solved in. Matching it is a perfect climb.
Inspired by Lewis Carroll's Doublets (1879)