5 instance Additive E where
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7 E a + E b = E ("(" + a + "+" + b + ")")
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9 instance Ring E where
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11 neg (E a) = E ("(-" + a + ")")
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12 E a - E b = E ("(" + a + "-" + b + ")")
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13 E a * E b = E ("(" + a + "*" + b + ")")
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14 fromInteger x = E (show x)
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23 main = eToString (-a + b + (-c*d))
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