Calling helper from a controller

Rails
1

I try to call a helper define inside the application_helper.rb but I
obtain an error.
Is it possible ?
There is an other way ?

Thanks

2

<%if @troll.nil? %>

I try to call a helper define inside the application_helper.rb but I
obtain an error.

Error text dump please.

Is it possible ?

Ever

There is an other way ?

mappy.fr ?