(defun c:tt (/ ss ssl el)
  (if (setq ss (ssget '((90 . 4))))
    (progn
      (setq ssl (sslength ss))
      (while (> ssl 0)
	(setq el (entget (ssname ss (setq ssl (1- ssl))))
	      el (vl-remove (assoc 10 el) el)
	      el (vl-remove (assoc 10 (reverse el)) el)
	      el (subst '(90 . 2) '(90 . 4) el)
	)
	(entmod el)
      )
    )
  )
  (princ)
)