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Planner (often seen in publications as "PLANNER" although it is not an acronym) is a programming language designed by Carl Hewitt at MIT, and first published in 1969. First, subsets such as MicroPlanner and PicoPlanner were implemented, and then essentially the whole language was implemented in Popler.^{[1]} Derivations such as QA4, Conniver, QLISP and Ether (see Scientific Community Metaphor) were important tools in Artificial Intelligence research in the 1970s, which influenced commercial developments such as KEE and ART.
Contents
Procedural Approach versus Logical Approach
The two major paradigms for constructing semantic software systems were procedural and logical. The procedural paradigm was epitomized by Lisp [McCarthy et al. 1962] which featured recursive procedures that operated on list structures.
The logical paradigm was epitomized by uniform proof procedure resolution theorem provers [Robinson 1965]. According to the logical paradigm it was “cheating” to incorporate procedural knowledge [Green 1969].
Procedural Embedding of Knowledge
Planner was invented for the purposes of the procedural embedding of knowledge [Hewitt 1971] and was a rejection of the resolution uniform proof procedure paradigm [Robinson 1965], which
Planner was a kind of hybrid between the procedural and logical paradigms because it combined programmability with logical reasoning. Planner featured a procedural interpretation of logical sentences where an implication of the form (P implies Q) can be procedurally interpreted in the following ways using patterndirected invocation:

 If assert P, assert Q
 If assert not Q, assert not P

 If goal Q, goal P
 If goal not P, goal not Q
In this respect, the development of Planner was influenced by natural deductive logical systems (especially the one by Frederic Fitch [1952]).
Microplanner implementation
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