OpenMath Content Dictionary: fns1

Canonical URL:
http://www.openmath.org/cd/fns1.ocd
CD File:
fns1.ocd
CD as XML Encoded OpenMath:
fns1.omcd
Defines:
domain, domainofapplication, identity, image, inverse, lambda, left_compose, left_inverse, range, right_inverse
Date:
2001-03-12
Version:
2
Review Date:
2003-04-01
Status:
official
Uses CD:
quant1, relation1, logic1, set1

This CD is intended to be `compatible' with the corresponding elements in Content MathML.

In this CD we give a set of functions concerning functions themselves. Functions can be constructed from expressions via a lambda expression. Also there are basic function functions like compose, etc.


domainofapplication

The domainofapplication element denotes the domain over which a given function is being applied. It is intended in MathML to be a more general alternative to specification of this domain using such quantifier elements as bvar, lowlimit or condition.

Signatures:
sts


[Next: domain] [Last: lambda] [Top]

domain

This symbol denotes the domain of a given function, which is the set of values it is defined over.

Commented Mathematical property (CMP):
x is in the domain of f if and only if there exists a y in the range of f and f(x) = y
Formal Mathematical property (FMP):
<OMOBJ>
  <OMA>
    <OMS cd="logic1" name="equivalent"/>
    <OMA>
      <OMS cd="set1" name="in"/>
      <OMV name="x"/>
      <OMA>
        <OMS cd="fns1" name="domain"/>
	<OMV name="f"/>
      </OMA>
    </OMA>
    <OMBIND>
      <OMS cd="quant1" name="exists"/>
      <OMBVAR>
        <OMV name="y"/>
      </OMBVAR>
      <OMA>
        <OMS cd="logic1" name="and"/>
        <OMA>
          <OMS cd="set1" name="in"/>
	  <OMV name="y"/>
	  <OMA>
            <OMS cd="fns1" name="range"/>
	    <OMV name="f"/>
	  </OMA>
        </OMA>
	<OMA>
	  <OMS cd="relation1" name="eq"/>
	  <OMA>
	    <OMV name="f"/>
	    <OMV name="x"/>
	  </OMA>
	  <OMV name="y"/>
	</OMA>
      </OMA>
    </OMBIND>
  </OMA>
</OMOBJ>

equivalent (in ( x, domain ( f) ) , exists [ y ] . (and (in ( y, range ( f) ) , eq ( f ( x) , y) ) ) )

Signatures:
sts


[Next: range] [Previous: domainofapplication] [Top]

range

This symbol denotes the range of a function, that is a set that the function will map to. The single argument should be the function whos range is being queried. It should be noted that this is not necessarily equal to the image, it is merely required to contain the image.

Commented Mathematical property (CMP):
the range of f is a subset of the image of f
Formal Mathematical property (FMP):
<OMOBJ>
  <OMA>
    <OMS cd="set1" name="subset"/>
    <OMA>
      <OMS cd="fns1" name="range"/>
      <OMV name="f"/>
    </OMA>
    <OMA>
      <OMS cd="fns1" name="image"/>
      <OMV name="f"/>
    </OMA>
  </OMA>
</OMOBJ>

subset (range ( f) , image ( f) )

Signatures:
sts


[Next: image] [Previous: domain] [Top]

image

This symbol denotes the image of a given function, which is the set of values the domain of the given function maps to.

Commented Mathematical property (CMP):
x in the domain of f implies f(x) is in the image f
Formal Mathematical property (FMP):
<OMOBJ>
  <OMA>
    <OMS cd="logic1" name="implies"/>
    <OMA>
      <OMS cd="set1" name="in"/>
      <OMV name="x"/>
      <OMA>
	<OMS cd="fns1" name="domain"/>
	<OMV name="f"/>
      </OMA>
    </OMA>
    <OMA>
      <OMS cd="set1" name="in"/>
      <OMA>
        <OMV name="f"/>
	<OMV name="x"/>
      </OMA>
      <OMA>
        <OMS cd="fns1" name="image"/>
	<OMV name="f"/>
      </OMA>
    </OMA>
  </OMA>
</OMOBJ>

implies (in ( x, domain ( f) ) , in ( f ( x) , image ( f) ) )

Signatures:
sts


[Next: identity] [Previous: range] [Top]

identity

The identity function, it takes one argument and returns the same value.

Commented Mathematical property (CMP):
for all x | identity(x)=x
Formal Mathematical property (FMP):
<OMOBJ>
  <OMBIND>
    <OMS cd="quant1" name="forall"/>
    <OMBVAR>
      <OMV name="x"/>
    </OMBVAR>
    <OMA>
      <OMS cd="relation1" name="eq"/>
      <OMA>
        <OMS cd="fns1" name="identity"/>
        <OMV name="x"/>
      </OMA>
      <OMV name="x"/>
    </OMA>
  </OMBIND>
</OMOBJ>

forall [ x ] . (eq (identity ( x) , x) )

Signatures:
sts


[Next: left_inverse] [Previous: image] [Top]

left_inverse

This symbol is used to describe the left inverse of its argument (a function). This inverse may only be partially defined because the function may not have been surjective. If the function is not surjective the left inverse function is ill-defined without further stipulations. No other assumptions are made on the semantics of this left inverse.

Signatures:
sts


[Next: right_inverse] [Previous: identity] [Top]

right_inverse

This symbol is used to describe the right inverse of its argument (a function). This inverse may only be partially defined because the function may not have been surjective. If the function is not surjective the right inverse function is ill-defined without further stipulations. No other assumptions are made on the semantics of this right inverse.

Signatures:
sts


[Next: inverse] [Previous: left_inverse] [Top]

inverse

This symbol is used to describe the inverse of its argument (a function). This inverse may only be partially defined because the function may not have been surjective. If the function is not surjective the inverse function is ill-defined without further stipulations. No assumptions are made on the semantics of this inverse.

Commented Mathematical property (CMP):
(inverse(f))(f(x)) = x if f is injective, that is (for all x,y | f(x) = f(y) implies x=y) implies (inverse(f))(f(z)) = z
Formal Mathematical property (FMP):
<OMOBJ>
<OMA>
  <OMS cd="logic1" name="implies"/>
  <OMBIND>
    <OMS cd="quant1" name="forall"/>
    <OMBVAR>
      <OMV name="x"/>
      <OMV name="y"/>
    </OMBVAR>
    <OMA>
      <OMS cd="logic1" name="implies"/>
      <OMA>
        <OMS cd="relation1" name="eq"/>
        <OMA>
          <OMV name="f"/>
	  <OMV name="x"/>
        </OMA>
        <OMA>
          <OMV name="f"/>
          <OMV name="y"/>
        </OMA>
      </OMA>
      <OMA>
        <OMS cd="relation1" name="eq"/>
        <OMV name="x"/>
        <OMV name="y"/>
      </OMA>
    </OMA>
  </OMBIND>
  <OMA>
    <OMS cd="relation1" name="eq"/>
    <OMA>
      <OMA>
        <OMS cd="fns1" name="inverse"/>
        <OMV name="f"/>
      </OMA>
      <OMA>
        <OMV name="f"/>
        <OMV name="z"/>
      </OMA>
    </OMA>
    <OMV name="z"/>
  </OMA>
</OMA>
</OMOBJ>

implies (forall [ x y ] . (implies (eq ( f ( x) , f ( y) ) , eq ( x, y) ) ) , eq (inverse ( f) ( f ( z) ) , z) )

Commented Mathematical property (CMP):
f(inverse(f(y))=y if f is defined at inverse(f)(y) that is, if there exists an x s.t. inverse(f)(y) = x then this implies f(inverse(f)(y)) = y
Formal Mathematical property (FMP):
<OMOBJ>
  <OMA>
    <OMS cd="logic1" name="implies"/>
    <OMA>
      <OMBIND>
        <OMS cd="quant1" name="exists"/>
	<OMBVAR>
	  <OMV name="x"/>
	</OMBVAR>
	<OMA>
	  <OMS cd="relation1" name="eq"/>
	  <OMA>
	    <OMA>
	      <OMS cd="fns1" name="inverse"/>
	      <OMV name="f"/>
	    </OMA>
	    <OMV name="y"/>
	  </OMA>
	  <OMV name="x"/>
	</OMA>
      </OMBIND>
    </OMA>
    <OMA>
      <OMS cd="relation1" name="eq"/>
      <OMA>
        <OMV name="f"/>
	<OMA>
	  <OMA>
	    <OMS cd="fns1" name="inverse"/>
	    <OMV name="f"/>
	  </OMA>
	  <OMV name="y"/>
	</OMA>
      </OMA>
      <OMV name="y"/>
    </OMA>
  </OMA>
</OMOBJ>

implies (exists [ x ] . (eq (inverse ( f) ( y) , x) ) () , eq ( f (inverse ( f) ( y) ) , y) )

Signatures:
sts


[Next: left_compose] [Previous: right_inverse] [Top]

left_compose

This symbol represents the function which forms the left-composition of its two (function) arguments.

Commented Mathematical property (CMP):
for all f,g,x | left_compose(f,g)(x) = f(g(x))
Formal Mathematical property (FMP):
<OMOBJ>
<OMBIND>
  <OMS cd="quant1" name="forall"/>
  <OMBVAR>
    <OMV name="f"/>
    <OMV name="g"/>
    <OMV name="x"/>
  </OMBVAR>
  <OMA>
    <OMS cd="relation1" name="eq"/>
    <OMA>
      <OMA>
        <OMS cd="fns1" name="left_compose"/>
        <OMV name="f"/>
        <OMV name="g"/>
      </OMA>
      <OMV name="x"/>
    </OMA>
    <OMA>
      <OMV name="f"/>
      <OMA>
        <OMV name="g"/>
        <OMV name="x"/>
      </OMA>
    </OMA>
  </OMA>
</OMBIND>
</OMOBJ>

forall [ f g x ] . (eq (left_compose ( f, g) ( x) , f ( g ( x) ) ) )

Signatures:
sts


[Next: lambda] [Previous: inverse] [Top]

lambda

This symbol is used to represent anonymous functions as lambda expansions. It is used in a binder that takes two further arguments, the first of which is a list of variables, and the second of which is an expression, and it forms the function which is the lambda extraction of the expression

Example:
An example to show the connection between curried and uncurried applications of a binary function f (lambda(x,y).(f))(a,b)= (lambda(x).((lambda(y).(f))(b)))(a)
<OMOBJ>
<OMBIND>
  <OMS cd="quant1" name="forall"/>
  <OMBVAR>
    <OMV name="a"/>
    <OMV name="b"/>
  </OMBVAR>
  <OMA>
    <OMS cd="relation1" name="eq"/>
    <OMA>
      <OMBIND>
        <OMS cd="fns1" name="lambda"/>
        <OMBVAR>
          <OMV name="x"/>
          <OMV name="y"/>
        </OMBVAR>
        <OMV name="f"/>
      </OMBIND>
      <OMV name="a"/>
      <OMV name="b"/>
    </OMA>
    <OMA>
      <OMBIND>
        <OMS cd="fns1" name="lambda"/>
        <OMBVAR>
          <OMV name="x"/>
        </OMBVAR>
        <OMA>
          <OMBIND>
            <OMS cd="fns1" name="lambda"/>
            <OMBVAR>
              <OMV name="y"/>
            </OMBVAR>
            <OMV name="f"/>
          </OMBIND>
          <OMV name="b"/>
        </OMA>
      </OMBIND>
      <OMV name="a"/>
    </OMA>
  </OMA>
</OMBIND>
</OMOBJ>

forall [ a b ] . (eq (lambda [ x y ] . ( f) ( a, b) , lambda [ x ] . (lambda [ y ] . ( f) ( b) ) ( a) ) )

Signatures:
sts


[First: domainofapplication] [Previous: left_compose] [Top]