unfold continuous_at, rat_limit in *.
intuition.
exists (minRat (c * (1 / 2)) (c * (1/2) * c * epsilon)).
intuition.
unfold minRat in *.
destruct (bleRat (c * (1 / 2)) (c * (1 / 2) * c * epsilon)).
apply ratMult_0 in H2; intuition.
apply ratMult_0 in H2; intuition.
apply ratMult_0 in H3; intuition.
apply ratMult_0 in H2; intuition.
rewrite H2.
rewrite H0.
assert (ratDistance x c <= c * (1/2)).
eapply leRat_trans.
eapply H3.
eapply minRat_le_l.
assert (ratSubtract c (c * (1/2)) <= x).
eapply ratDistance_ge_difference.
rewrite ratDistance_comm.
trivial.
assert (x <= c + (c * (1/2))).
eapply ratDistance_le_sum.
trivial.
assert (c * (1/2) <= x).
rewrite <- (ratSubtract_half).
trivial.
clear H5.
assert (x <= c * (3/2)).
rewrite ratMult_ratAdd_cd in H6.
simpl in *.
trivial.
clear H6.
assert (ratInverse x <= ratInverse (c * (1 / 2))).
apply ratInverse_leRat.
intuition.
apply ratMult_0 in H6; intuition.
trivial.
rewrite ratDistance_ratInverse.
rewrite H3.
rewrite minRat_le_r.
rewrite ratInverse_ratMult; intuition.
rewrite H6.
rewrite ratInverse_ratMult; intuition.
rewrite ratMult_comm.
repeat rewrite <- ratMult_assoc.
rewrite (ratMult_assoc ((ratInverse c) * (ratInverse (1/2)))).
rewrite ratInverse_prod_1; intuition.
rewrite ratMult_1_r.
rewrite (ratMult_assoc (ratInverse c)).
rewrite ratInverse_prod_1; intuition.
rewrite ratMult_1_r.
rewrite ratInverse_prod_1; intuition.
rewrite ratMult_1_l.
intuition.
rewrite H8 in H7.
assert (c * (1 / 2) == 0).
eapply leRat_impl_eqRat.
trivial.
eapply rat0_le_all.
apply ratMult_0 in H9; intuition.
intuition.
rewrite H8 in H7.
assert (c * (1 / 2) == 0).
eapply leRat_impl_eqRat.
trivial.
eapply rat0_le_all.
apply ratMult_0 in H9; intuition.
intuition.
Qed.

Lemma rat_inf_limit_ratInverse : forall (f : nat -> Rat -> Prop) a v,
rat_inf_limit f a ->
~ a == 0 ->
ratInverse a == v ->
left_total f ->
rat_inf_limit (fun n => ratInverse_rel (f n)) v.