I have an expression ((((((P o Q) o R) o S) o T) o U) o V) where "o" is associative. I want to write a strategy to be able to concentrate on some subterm in the middle (for example (S o T o U)) and rewrite it using some hypothesys (for example S o T o U = A o B). Any help would be appreciated. Best regards, Viorel Preoteasa