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;;; Problem 2
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;;; Problem 2
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(defun PALINDROMEP (LI)
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(defun PALINDROMEP (LI)
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  ; define a local function so we can do this tail-recursively
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  ; define a local function so we can do this tail-recursively
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  (labels ((PAL-HELP (L1 L2)
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  (labels ((PAL-HELP (L1 L2)
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              (cond
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              (cond
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                ((null L1) t)
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                ((null L1)                 t)
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                ((equal (car L1) (car L2)) (PAL-HELP (cdr L1) (cdr L2)))
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                ((equal (car L1) (car L2)) (PAL-HELP (cdr L1) (cdr L2)))
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                (t                        nil)
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                (t                         nil)
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              )
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              )
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            ))
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            ))
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    ; call the tail-recursive local function
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    ; call the tail-recursive local function
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    (PAL-HELP LI (reverse LI))
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    (PAL-HELP LI (reverse LI))
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  )
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  )