Execute LISP Online

(defun triangle (a)
    (cond
        ((stringp a)
            (format t "strings are not valid input, please enter an integer")
        )
        ((not (numberp a))
            (format t "please enter an integer greater or equal to 1")
        )
        ((and (> a 0) (integerp a))
            (dotimes (row a)
                (print 1)
                (if (> a 1)
                    (dotimes (column row)
                        (write (+ column 2))
                        (format t " ")
                    )
                )
            )
        )
        ((and (< a 1) (integerp a))
            (format t "integers less than 1 are not valid input, please enter an integer greater or equal to 1")
        )
        ((numberp a) 
            (format t "decimal numbers are not valid input, please enter an integer")
        )
    )
)
(triangle 'a)