Solutions to selecta week2
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Recursion

1.	

(define (expt base power)
	(if (= power 0)
	    1
            (* base (expt base (- power 1)))))


2.


(define (count-ways n m)
	(cond ((or (= n 0) (= m 0)) 1)
	      (else (+ (count-ways n (- m 1))
		       (count-ways (- n 1) m)))))


3.	

(define (subsent sent i)
	(cond ((= i 0) sent)
	      (else (subsent (bf sent) (- i 1)))))



6.	

(define (sum-of-sents s1 s2)
	(cond ((empty? s1) s2)
	      ((empty? s2) s1)
	      (else (se (+ (first s1) (first s2))
		        (sum-of-sents (bf s1) (bf s2))))))