/// <summary>
 /// Appends a self-resolving operator to the expression and
 /// returns a new ResolvableConstraintExpression.
 /// </summary>
 public ResolvableConstraintExpression Append(SelfResolvingOperator op)
 {
     builder.Append(op);
     return(new ResolvableConstraintExpression(builder));
 }
 /// <summary>
 /// Appends a self-resolving operator to the expression and
 /// returns a new ResolvableConstraintExpression.
 /// </summary>
 public ResolvableConstraintExpression Append(SelfResolvingOperator op)
 {
     builder.Append(op);
     return new ResolvableConstraintExpression(builder);
 }