-- | The polarity of the literal.  Negative literals are false; positive
-- literals are true.  The 0-literal is an error.
litSign :: Lit -> Bool
litSign (L x) | x < 0     = False
              | x > 0     = True
              | otherwise = error "litSign of 0"
litSign :: Lit -> Bool
litSign (L x) | x < 0     = False
              | x > 0     = True
              | otherwise = error "litSign of 0"
litSign (L x) | x < 0     = False
              | x > 0     = True
              | otherwise = error "litSign of 0"