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LISP I Programmer's Manual - Software Preservation Group

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The answer ( ((x A) B) (X A) ) will be printed,3.3 DebuggingThe main debugging tool is the pseudo-function tracklist.If you put a cardTRACKLIST (fi fp ... fn) (>after the cards which define the functions fl, ..., fn and beforethe functions are used in computations, the computer will printthe arguments and values of fl,,..,fn each time they are usedrecursively in a computation, tracklist acts as a tracing program,but usually it is not necessary to trace more than one ortwo functions.3.4 The Wang Algorithm for the Propositional CalculusAs an extended example of the use of a succession of functiondefinitions to define an algorithm we give a <strong>LISP</strong> formulationof an algorithm for deciding whether a formula is a theoremof the propositional calculus published recently by Hao Wang. 1Readers completely unacquainted with propositional calculusshould probably skip this example,1Wang, Hao . "~oward Mechanical at he ma tics " , IBM Journal ofResearch and Development, Vol. 4, No. 1, January 1960

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