Forum:T.G. Hyper Librarian versus Trishula or Black Rose D.

If I invoke Trishula or Black Rose Dragon and destroy or remove T.G. Hyper Librarian respectively, my opponent may draw a card for the effect of T.G. Hyper Librarian?

I understand that I have the effect of T.G. Hyper Librarian is mandatory and begins a chain and the effect of Black Rose Dragon Trishula or is not mandatory.

On the other hand the effect of T.G. Hyper Librarian applies when your back on the field.

Please can I explain this in detail ...