x + 3 < 7
x < 7 - 3
x < 4
A={0,1,2,3}
B={0, 10,20,30,40,50,60, ...}
A intersectat cu B = {0}
B\A = {10,20,30,40,50,60, ...}
A reunit cu B = {0,1,2,3,10,20,30,40,50, ...}
A\B = {1,2,3}
