Obstruent voiced obstruents are common. This contrasts with sonorants, which are prototypically voiced and only rarely voiceless. Obstruent An obstruent is a speech sound such as , , or that is formed by "obstructing" airflow. Obstruents contrast with sonorants, which have no such obstruction and so resonate. All obstruents are consonants, but sonorants include both vowels and consonants. Obstruents are subdivided into plosives (oral stops), such as , with complete occlusion of the vocal tract, often followed by a release burst; fricatives, such as , with limited closure, not stopping airflow but making it turbulent; and affricates, which begin with complete
Closure with a twist Closure with a twist Closure with a twist is a property of subsets of an algebraic structure. A subset formula_1 of an algebraic structure formula_2 is said to exhibit closure with a twist if for every two elements there exists an automorphism formula_4 of formula_2 and an element formula_6 such that where "formula_8" is notation for an operation on formula_2 preserved by formula_4. Two examples of algebraic structures which exhibit closure with a twist are the cwatset and the generalized cwatset, or GC-set. In mathematics, a cwatset is a set of bitstrings, all of the same length, which is closed