@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (!(obj instanceof Literal))
			return false;
		Literal other = (Literal) obj;
		if (sign != other.sign)
			return false;
		if (variable == null) {
			if (other.variable != null)
				return false;
		} else if (!variable.equals(other.variable))
			return false;
		return true;
	}