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(-1/4)*(0-12)+(1/2)*(0+21) = 0+4
(1/2)*(0+21)-1/4*(0-12) = 4
(1/2)*(0+21)-12*(-1/4) = 4
1/4*12+(1/2)*(0+21) = 4
(1/2)*(0+21)+3 = 4
1/2*(0+21)+3 = 4
1/2*21+3 = 4
3+21/2 = 4
27/2 = 4
L <> R
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