(VAR f l r x )
(RULES 
        app(app(mapbt,f),app(leaf,x)) -> app(leaf,app(f,x))
        app(app(mapbt,f),app(app(app(branch,x),l),r)) -> app(app(app(branch,app(f,x)),app(app(mapbt,f),l)),app(app(mapbt,f),r))
        
)