Sentence:  And the more complex the morphophonemic system <WSD>is</WSD> in relation to the phonemic base , the less easily a phonemic system will be analysed without close attention to the morphophonemics - at least , the less satisfying will a phonemic statement be if it cannot be related through morphophonemic rules to grammatically meaningful structures . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)