Few tasks are so new as to require the invention of strategies that have never been used by the task performer. Hence, in many situations, settling on a strategy or set of strategies for performing a task is not so much a matter of learning new strategies as it is learning which strategy, out of a set of already acquired strategies, is best adapted to the current environment. Blocks World is a simple task that has been used to study the tradeoff bnetween interaction-intensive and memory-intensive strategies.