+lemma flt_plusl:
+ ∀G:pogroup.∀x,y,z:G.x < y → z + x < z + y.
+intros (G x y z H); cases H; split; [apply fle_plusl; assumption]
+apply fap_plusl; assumption;
+qed.
+
+lemma flt_plusr:
+ ∀G:pogroup.∀x,y,z:G.x < y → x + z < y + z.
+intros (G x y z H); cases H; split; [apply fle_plusr; assumption]
+apply fap_plusr; assumption;
+qed.
+
+
+lemma ltxy_ltyyxx: ∀G:pogroup.∀x,y:G. y < x → y+y < x+x.
+intros; apply (lt_transitive ?? (y+x));[2:
+ apply (Lt≪? (plus_comm ???));
+ apply (Lt≫? (plus_comm ???));]
+apply flt_plusl;assumption;
+qed.
+
+lemma lew_opp : ∀O:pogroup.∀a,b,c:O.0 ≤ b → a ≤ c → a + -b ≤ c.
+intros (O a b c L0 L);
+apply (le_transitive ????? L);
+apply (plus_cancl_le ??? (-a));
+apply (Le≫ 0 (opp_inverse ??));
+apply (Le≪ (-a+a+-b) (plus_assoc ????));
+apply (Le≪ (0+-b) (opp_inverse ??));
+apply (Le≪ (-b) (zero_neutral ?(-b)));
+apply le_zero_x_to_le_opp_x_zero;
+assumption;
+qed.
+
+lemma ltw_opp : ∀O:pogroup.∀a,b,c:O.0 < b → a < c → a + -b < c.
+intros (O a b c P L);
+apply (lt_transitive ????? L);
+apply (plus_cancl_lt ??? (-a));
+apply (Lt≫ 0 (opp_inverse ??));
+apply (Lt≪ (-a+a+-b) (plus_assoc ????));
+apply (Lt≪ (0+-b) (opp_inverse ??));
+apply (Lt≪ ? (zero_neutral ??));
+apply lt_zero_x_to_lt_opp_x_zero;
+assumption;
+qed.
+
+record togroup : Type ≝ {
+ tog_carr:> pogroup;
+ tog_total: ∀x,y:tog_carr.x≰y → y < x
+}.
+
+lemma lexxyy_lexy: ∀G:togroup. ∀x,y:G. x+x ≤ y+y → x ≤ y.
+intros (G x y H); intro H1; lapply (tog_total ??? H1) as H2;
+lapply (ltxy_ltyyxx ??? H2) as H3; lapply (lt_to_excess ??? H3) as H4;
+cases (H H4);
+qed.
+
+lemma eqxxyy_eqxy: ∀G:togroup.∀x,y:G. x + x ≈ y + y → x ≈ y.
+intros (G x y H); cases (eq_le_le ??? H); apply le_le_eq;
+apply lexxyy_lexy; assumption;
+qed.
+
+lemma applus_orap: ∀G:abelian_group. ∀x,y:G. 0 # x + y → 0 #x ∨ 0#y.
+intros; cases (ap_cotransitive ??? y a); [right; assumption]
+left; apply (plus_cancr_ap ??? y); apply (Ap≪y (zero_neutral ??));
+assumption;
+qed.
+
+lemma ltplus: ∀G:pogroup.∀a,b,c,d:G. a < b → c < d → a+c < b + d.
+intros (G a b c d H1 H2);
+lapply (flt_plusr ??? c H1) as H3;
+apply (lt_transitive ???? H3);
+apply flt_plusl; assumption;
+qed.
+
+lemma excplus_orexc: ∀G:pogroup.∀a,b,c,d:G. a+c ≰ b + d → a ≰ b ∨ c ≰ d.
+intros (G a b c d H1 H2);
+cases (exc_cotransitive ??? (a + d) H1); [
+ right; apply (plus_cancl_exc ??? a); assumption]
+left; apply (plus_cancr_exc ??? d); assumption;
+qed.
+
+lemma leplus: ∀G:pogroup.∀a,b,c,d:G. a ≤ b → c ≤ d → a+c ≤ b + d.
+intros (G a b c d H1 H2); intro H3; cases (excplus_orexc ????? H3);
+[apply H1|apply H2] assumption;
+qed.
+
+lemma leplus_lt_le: ∀G:togroup.∀x,y:G. 0 ≤ x + y → x < 0 → 0 ≤ y.
+intros; intro; apply H; lapply (lt_to_excess ??? l);
+lapply (tog_total ??? e);
+lapply (tog_total ??? Hletin);
+lapply (ltplus ????? Hletin2 Hletin1);
+apply (Ex≪ (0+0)); [apply eq_sym; apply zero_neutral]
+apply lt_to_excess; assumption;
+qed.
+
+lemma ltplus_orlt: ∀G:togroup.∀a,b,c,d:G. a+c < b + d → a < b ∨ c < d.
+intros (G a b c d H1 H2); lapply (lt_to_excess ??? H1);
+cases (excplus_orexc ????? Hletin); [left|right] apply tog_total; assumption;
+qed.
+
+lemma excplus: ∀G:togroup.∀a,b,c,d:G.a ≰ b → c ≰ d → a + c ≰ b + d.
+intros (G a b c d L1 L2);
+lapply (fexc_plusr ??? (c) L1) as L3;
+elim (exc_cotransitive ??? (b+d) L3); [assumption]
+lapply (plus_cancl_exc ???? t); lapply (tog_total ??? Hletin);
+cases Hletin1; cases (H L2);
+qed.