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• Sin$c

Sin$c-firstn

Concrete implementation of strin-firstn.

Signature

(sin$c-firstn n sin$c) → *

Arguments

n — Guard (natp n).

sin$c — Guard (sin$c-okp sin$c).

Definitions and Theorems

Function: sin$c-firstn

(defun sin$c-firstn (n sin$c)
  (declare (xargs :stobjs (sin$c)))
  (declare (xargs :guard (and (natp n) (sin$c-okp sin$c))))
  (declare (xargs :guard (<= n (sin$c-len sin$c))))
  (let ((__function__ 'sin$c-firstn))
    (declare (ignorable __function__))
    (b* (((the string str) (sin$c-str sin$c))
         ((the (unsigned-byte 60) pos)
          (sin$c-pos sin$c))
         ((the (unsigned-byte 60) len)
          (length str))
         ((the (unsigned-byte 60) stop)
          (+ pos (the (unsigned-byte 60) n))))
      (the string
           (subseq (the string str) pos stop)))))

Theorem: sin-firstn{correspondence}

(defthm sin-firstn{correspondence}
  (implies (and (sin$corr sin$c sin)
                (natp n)
                (strin-p sin)
                (<= n (strin-len sin)))
           (equal (sin$c-firstn n sin$c)
                  (strin-firstn n sin))))