cu '=' notez <-
a) s1, s3, s2
s1 : a = 1, b = 2, c = 3 , d = 4
s3 : a = 3, b = 3 ,c = 4 , d = 1
s2 : a = 3, b = 4 ,c = 1 , d = 3
b) s1,s2,s3,s4
s1 : a = 1 ,b = 2 , c = 3 , d = 4
s2 : a = 2 ,b = 3 , c = 4 , d = 2
s3 : a = 4 ,b = 4 , c = 2 , d = 2
s4 : a = 4 ,b = 2 , c = 2 , d = 4
c) s1,s2,s2,s3
s1 : a = 1 ,b = 2 , c = 3 , d = 4
s2 : a = 2 ,b = 3 , c = 4 , d = 2
s2 : a = 3 ,b = 4 , c = 2 , d = 3
s3 : a = 2 ,b = 2 , c = 3 , d = 3