Definition is_finite f :=
match f with
| B754_finite _ _ _ _ => true
| B754_zero _ => true
| _ => false
end.
Definition is_finite_FF f :=
match f with
| F754_finite _ _ _ => true
| F754_zero _ => true
| _ => false
end.

Theorem is_finite_FF2B :
forall x Hx,
is_finite (FF2B x Hx) = is_finite_FF x.