/// <summary>
/// Initializes a new instance of the <see cref="Clause"/> class.
/// </summary>
///
/// <param name="variable">Linguistic variable of the clause. </param>
///
/// <param name="label">Label of the linguistic variable, a fuzzy set used as label into the linguistic variable.</param>
///
/// <exception cref="KeyNotFoundException">The label indicated was not found in the linguistic variable.</exception>
///
public Clause(LinguisticVariable variable, FuzzySet label)
{
// check if label belongs to var.
variable.GetLabel(label.Name);
// initializing attributes
this.label = label;
this.variable = variable;
}