** Danube ruffe, Gymnocephalus baloni.

** Ruffe, Gymnocephalus cernuus.

** Schraetzer, Gymnocephalus schraetser.

** Eunectes murinus, the green anaconda, the largest species, is found east of the Andes in Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil and on the island of Trinidad.

** Eunectes notaeus, the yellow anaconda, a smaller species, is found in eastern Bolivia, southern Brazil, Paraguay and northeastern Argentina.

** Eunectes deschauenseei, the dark-spotted anaconda, is a rare species found in northeastern Brazil and coastal French Guiana.

** Eunectes beniensis, the Bolivian anaconda, the most recently defined species, is found in the Departments of Beni and Pando in Bolivia.

** Well-ordering theorem: Every set can be well-ordered.

** Tarski's theorem: For every infinite set A, there is a bijective map between the sets A and A × A.

** Trichotomy: If two sets are given, then either they have the same cardinality, or one has a smaller cardinality than the other.

** The Cartesian product of any family of nonempty sets is nonempty.

** König's theorem: Colloquially, the sum of a sequence of cardinals is strictly less than the product of a sequence of larger cardinals.

** Every surjective function has a right inverse.

** Zorn's lemma: Every non-empty partially ordered set in which every chain ( i. e. totally ordered subset ) has an upper bound contains at least one maximal element.

** Hausdorff maximal principle: In any partially ordered set, every totally ordered subset is contained in a maximal totally ordered subset.

** Tukey's lemma: Every non-empty collection of finite character has a maximal element with respect to inclusion.

** Antichain principle: Every partially ordered set has a maximal antichain.

** Every vector space has a basis.

** Every unital ring other than the trivial ring contains a maximal ideal.

** For every non-empty set S there is a binary operation defined on S that makes it a group.

** The closed unit ball of the dual of a normed vector space over the reals has an extreme point.

** Tychonoff's theorem stating that every product of compact topological spaces is compact.

** In the product topology, the closure of a product of subsets is equal to the product of the closures.

** If S is a set of sentences of first-order logic and B is a consistent subset of S, then B is included in a set that is maximal among consistent subsets of S. The special case where S is the set of all first-order sentences in a given signature is weaker, equivalent to the Boolean prime ideal theorem ; see the section " Weaker forms " below.

** Any union of countably many countable sets is itself countable.

The western region has the Carpathian Mountains, the Crimean Peninsula has the Crimean Mountains, and some eroded mountains from the Donets Ridge are in the east near the Sea of Azov.

Ukraine's various highland regions include the Volyn-Podillia Upland and the Near-Dnipro Upland ( on the right bank of Dnipro River ) in the west, the south-western spurs of the Central Russian Uplands upon which runs the border with Russia in the east, and the Donets Ridge and the Near Azov Upland near the Sea of Azov.

There are seven major rivers in Ukraine: Desna, Dnipro, Dnister, Danube, Prypiat, Siverian Donets, and Southern Buh.

This country was situated between the lower course of the Danube river to the west, the Black Sea and the Azov Sea to the south, the Kuban river to the east and the Donets river to the north.

Its main tributary is the Donets.

The Kochetovsky Lock, built in 1914-1919 and doubled in 2004-2008, is located 7. 5 km below the fall of the Seversky Donets into the Don, and 131 km upstream of Rostov-na-Donu, the Kochetovsky Ship Lock ( Кочетовский гидроузел ) () is located.

This facility, with its dam, maintains sufficient water level both in its section of the Don and in the lowermost stretch of the Seversky Donets.

* Seversky Donets ( 1. 053 km )

On 6 January 1481, the Khan was killed by Ibak Khan, the prince of Tyumen, and Nogays at the mouth of the Donets River.

But the German armies could not rest, for fear the Soviet southern armies ( now commanded by the stubborn Marshal Semyon Timoshenko ) would regroup and consolidate a front on the Donets or the Don.

Reichenau advanced east towards Kharkov and Kleist and Stülpnagel headed south-east towards the lower Donets.

The eastern and southern borders of the tribe's habitat were never permanent and would sometimes reach the upper reaches of the Seversky Donets.

Known to the Germans as the Donets Campaign, and to the Soviets as the Donbas and Kharkov operations, the German counterstrike led to the destruction of approximately 52 Soviet divisions and the recapture of the cities of Kharkov and Belgorod.

A Soviet drive, spearheaded by four tank corps organized under Lieutenant-General Markian Popov, pierced the German front by crossing the Donets River and pressing into the German rear.

In conjunction with Operation Star the Soviets also launched Operation Gallop south of Star, pushing the Germans away from the Donets, taking Voroshilovgrad and Izium, worsening the German situation further.

On 20 February, the Red Army was perilously close to Zaporizhia, signaling the beginning of the German counterattack, known to the Germans as the Donets Campaign.

What was known to the Germans as the Donets Campaign took place between 19 February and 15 March 1943.

The First Panzer Army was able to regain a defensive line on the Donets River, and Manstein began to plan subsequent attacks to clear Soviet units west of the Donets.

Army Group South's Donets Campaign had cost the Red Army some 52 divisions, including over 70, 000 – 80, 000 personnel casualties.

On 14 – 15 March these forces were given permission to withdraw to the northern Donets River.

After the fall of Kharkov the Soviet defense of the Donets had collapsed, allowing Manstein's forces to drive to Belgorod on 17 March, and take it by the next day.

The lowest point is located at the bottom of the Oskol and Seversky Donets River valleys.