1)a-b-2c-d-f
2)a-b+c-d+c-f=a-b+2c-d-f
3)a+b-c+d-c+f=a+b-2c+d+f
4)a+b-c+d-c+f=a+b-2c+d+f
5)a+b+c-d+c+f=a+b+2c-d+f
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