Okay, you two. Stop bickering please. A variety of approaches to explaining things is welcome here.
Some people relate to the jargon, others don't, but there is no need for anyone to be snarky about how other people try to explain something.
The fact is that
bí, like common verbs in many languages, has become an assemblage of several verb parts:
bí "to be";
tá, which originally meant "to stand"; and
fuil, which is an old dependent form. So whether it is one verb or several verbs depends on how you look at it.
The negative of
tá is
níl, which comes from
ní fhuil. The
fh is silent and the two
i sounds on either side have elided together to form one word.
For the difference between
tá and
bíonn, consider the following two sentences:
Tá sé fuar i nDoire anocht. "It is cold in Derry tonight." (An actual occurrence)
Bíonn sé fuar i nDoire sa gheimhreadh. "It is cold in Derry in the winter." (A tendency)