Sorry it took me more than 2 years to answer this.
In short : you don't need the underscore, defining and using a variable named Y1 will result as if it was Y_1
This is now explained in the documentation
Sorry it took me more than 2 years to answer this.
In short : you don't need the underscore, defining and using a variable named Y1 will result as if it was Y_1
This is now explained in the documentation