Fundamental Theorem of Algebra

Let n:nat and f be a complex polynomial of degree (S n).

Section FTA_reg'.

Variable f : cpoly_cring C.
Variable n : N.
Hypothesis f_degree : degree (S n) f.

Lemma FTA_reg' : {f1 : C[X] | degree 1 f1 | {f2 : C[X] | degree n f2 | f [=] f1[*]f2}}.








End FTA_reg'.

Let n:nat, f be a complex polynomial of degree less than or equal to (S n) and c be a complex number such that f!c [#] 0.

Section FTA_1.

Variable f : cpoly_cring C.
Variable n : N.
Hypothesis f_degree : degree_le (S n) f.
Variable c : C.
Hypothesis f_c : f ! c [#] 0.

Lemma FTA_1a : degree_le (S n) (Shift c f).

Let g := Rev (S n) (Shift c f).

Lemma FTA_1b : degree (S n) g.


Lemma FTA_1 : {f1 : C[X] | {f2 : C[X] | degree_le 1 f1 /\ degree_le n f2 /\ f [=] f1[*]f2}}.








Lemma FTA_1' : {a : C | {b : C | {g : C[X] | degree_le n g | f [=] (_C_ a[*]_X_[+]_C_ b) [*]g}}}.








End FTA_1.

Section Fund_Thm_Alg.

Lemma FTA' : forall n (f : C[X]), degree_le n f -> nonConst _ f -> {z : C | f ! z [=] 0}.



















Lemma FTA : forall f : C[X], nonConst _ f -> {z : C | f ! z [=] 0}.


Lemma FTA_a_la_Henk : forall f : C[X],
 {x : C | {y : C | AbsCC (f ! x[-]f ! y) [>]0}} -> {z : C | f ! z [=] 0}.

End Fund_Thm_Alg.