** H < sub > 2 </ sub > O ( l ) + 240kJ → H < sub > 2 </ sub > O ( g )

** O Sapientia ( Roman Catholic Church )

** O Adonai

** O Rex

** O Radix

** O Clavis

** O Oriens

** O Uraguai by Basílio da Gama ( 1769 )

** Serial I / O (" Link cable "): 512 kbit / s with up to 4 connections in serial

** Infra-red I / O: Less than 2 m distance at 45 °

** Cartridge I / O

** Improved InnoDB I / O subsystem

** Malachy O ' More

** in notation related to Big O notation to describe the asymptotic behavior of functions.

** In notation related to Big O notation, the asymptotically dominant nature of functions

** I / O Port Interface and Control

** Asynch and Synch I / O

** A doubly linked list has O ( 1 ) insertion and deletion at both ends, so is a natural choice for queues.

** nitrous oxide ( N < sub > 2 </ sub > O ; " NOS ", " Laughing Gas ", " Whippets ", " Balloons ")

** " Using Samba "- E-book ( Published by O ' Reilly as ISBN 0-596-00256-4 )

** Spinel: MgAl < sub > 2 </ sub > O < sub > 4 </ sub >, after which this class of minerals is named

** Gahnite: ZnAl < sub > 2 </ sub > O < sub > 4 </ sub >

** Hercynite: FeAl < sub > 2 </ sub > O < sub > 4 </ sub >

** Cuprospinel: CuFe < sub > 2 </ sub > O < sub > 4 </ sub >

** 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.