In
mathematical
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
writing, the term strict refers to the property of excluding equality and equivalence and often occurs in the context of
inequality
Inequality may refer to:
Economics
* Attention inequality, unequal distribution of attention across users, groups of people, issues in etc. in attention economy
* Economic inequality, difference in economic well-being between population groups
* ...
and
monotonic functions.
It is often attached to a technical term to indicate that the exclusive meaning of the term is to be understood. The opposite is non-strict, which is often understood to be the case but can be put explicitly for clarity. In some contexts, the word "proper" can also be used as a mathematical synonym for "strict".
Use
This term is commonly used in the context of
inequalities
Inequality may refer to:
Economics
* Attention inequality, unequal distribution of attention across users, groups of people, issues in etc. in attention economy
* Economic inequality, difference in economic well-being between population groups
* ...
— the phrase "strictly less than" means "less than and not equal to" (likewise "strictly greater than" means "greater than and not equal to").
More generally, a
strict partial order
In mathematics, especially order theory, a partially ordered set (also poset) formalizes and generalizes the intuitive concept of an ordering, sequencing, or arrangement of the elements of a set. A poset consists of a set together with a binary r ...
,
strict total order, and
strict weak order
In mathematics, especially order theory, a weak ordering is a mathematical formalization of the intuitive notion of a ranking of a set, some of whose members may be tied with each other. Weak orders are a generalization of totally ordered set ...
exclude equality and equivalence.
When comparing numbers to zero, the phrases "strictly positive" and "strictly negative" mean "positive and not equal to zero" and "negative and not equal to zero", respectively. In the context of functions, the adverb "strictly" is used to modify the terms "monotonic", "increasing", and "decreasing".
On the other hand, sometimes one wants to specify the inclusive meanings of terms. In the context of comparisons, one can use the phrases "non-negative", "non-positive", "non-increasing", and "non-decreasing" to make it clear that the inclusive sense of the terms is being used.
The use of such terms and phrases helps avoid possible ambiguity and confusion. For instance, when reading the phrase "''x'' is positive", it is not immediately clear whether ''x'' = 0 is possible, since some authors might use the term ''positive'' loosely to mean that ''x'' is not less than zero. Such an ambiguity can be mitigated by writing "''x'' is strictly positive" for ''x'' > 0, and "''x'' is non-negative" for ''x'' ≥ 0. (A precise term like ''non-negative'' is never used with the word ''negative'' in the wider sense that includes zero.)
The word "proper" is often used in the same way as "strict". For example, a "
proper subset
In mathematics, set ''A'' is a subset of a set ''B'' if all elements of ''A'' are also elements of ''B''; ''B'' is then a superset of ''A''. It is possible for ''A'' and ''B'' to be equal; if they are unequal, then ''A'' is a proper subset of ...
" of a
set
Set, The Set, SET or SETS may refer to:
Science, technology, and mathematics Mathematics
*Set (mathematics), a collection of elements
*Category of sets, the category whose objects and morphisms are sets and total functions, respectively
Electro ...
''S'' is a
subset that is not equal to ''S'' itself, and a "
proper class" is a class which is not also a set.
See also
*
Strictly positive measure
In mathematics, strict positivity is a concept in measure theory. Intuitively, a strictly positive measure is one that is "nowhere zero", or that is zero "only on points".
Definition
Let (X, T) be a Hausdorff topological space and let \Sigma be ...
*
Monotonic function
In mathematics, a monotonic function (or monotone function) is a function between ordered sets that preserves or reverses the given order. This concept first arose in calculus, and was later generalized to the more abstract setting of order ...
*
Mod about non-strict monotonic distribution.
References
{{PlanetMath attribution, id=6397, title=strict
Mathematical terminology