a. A guarantee is by its nature independent of the underlying relationship and the application, and the guarantor is in no way concerned with or bound by such relationship. A reference in the guarantee to the underlying relationship for the purpose of identifying it does not change the independent nature of the guaran- tee. The undertaking of a guarantor to pay under the guarantee is not subject to claims or defences arising from any relationship other than a relationship be- tween the guarantor and the beneficiary.