prolog: reduce then write the value of a predicate -

This is some code I'm writing

  emphasis (bar (foo)) , (FU (bar-5)),  

I'm not sure that it works though. I'm trying to reduce it by 5 foo. I want a way to write the value of Fu, but I have not found any way. Write ('Efu '+ Foo) would be a logical way for me, but it does not seem to work.

To be able to use the value of a fact, you have to first unify it to integrate, ungraded Variables are passed as a logic for a wordlist, - bar (mu) in our case:

  facts bar (integer) foo (integer) (Target) (bar (42)), bar (m), falcon = mo - 5, emphasis (fu (falcon)), write (falcon).