Sentence:  In order to focus clearly upon the operation of this one force , which we may call the effect of `` public limit pricing '' on `` key '' wage <WSD>bargains</WSD> , we deliberately simplify the model by abstracting from other forces , such as union power , which may be relevant in an actual situation . 
Meaning of the word marked with <WSD> tags:  an agreement between parties (usually arrived at after discussion) fixing obligations of each