/// <summary>
/// Differentiates the specified expression.
/// </summary>
/// <param name="expression">The expression.</param>
/// <param name="variable">The variable.</param>
/// <returns>Returns the derivative.</returns>
protected virtual IExpression Exp(Exp expression, Variable variable)
{
return new Mul(_Differentiate(expression.Argument.Clone(), variable), expression.Clone());
}
