Write tail-recursive versions of the following: (a) ;; compute integer log, base 2 ;; (number of bits in binary representation) ;; works only for positive integers (define log2 (lambda (n) (if (= n 1) 1 (+ 1 (log2 (quotient n 2)))))) (b) ;; find minimum element in a list (define min (lambda (l) (cond ((null? l) '()) ((null? (cdr l)) (car l)) (#t (let ((a (car l)) (b (min (cdr l)))) (if (< b a) b a))))))