<html><head><title>[CRISP] 6 Examples of group classes</title></head>
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<h1>6 Examples of group classes</h1><p>
<P>
<H3>Sections</H3>
<oL>
<li> <A HREF="CHAP006.htm#SECT001">Pre-defined group classes</a>
<li> <A HREF="CHAP006.htm#SECT002">Pre-defined projector functions</a>
<li> <A HREF="CHAP006.htm#SECT003">Pre-defined sets of primes</a>
</ol><p>
<p>
This chapter describes some pre-defined
group classes, namely the classes of all abelian, nilpotent, and supersoluble
groups. Moreover, there are some functions constructing the classes of all
<var>p</var>-groups, <var>pi</var>-groups, and abelian groups whose exponent divides a given
positive integer.
<p>
The definitions of these group classes can also serve as further examples of
how group classes can be defined using the methods described in the preceding
chapters.
<p>
<p>
<h2><a name="SECT001">6.1 Pre-defined group classes</a></h2>
<p><p>
<a name = "SSEC001.1"></a>
<li><code>TrivialGroups V</code>
<p>
<a name = "I0"></a>
<a name = "I1"></a>
<a name = "I2"></a>
The global variable <code>TrivialGroups</code> contains the class of all trivial groups. It is a
subgroup closed saturated Fitting formation.
<p>
<a name = "SSEC001.2"></a>
<li><code>NilpotentGroups V</code>
<p>
<a name = "I3"></a>
<a name = "I4"></a>
<a name = "I5"></a>
This global variable contains the class of all finite nilpotent groups. It is a
subgroup closed saturated Fitting formation.
<p>
<a name = "SSEC001.3"></a>
<li><code>SupersolubleGroups V</code>
<li><code>SupersolvableGroups V</code>
<p>
<a name = "I6"></a>
<a name = "I7"></a>
<a name = "I8"></a>
<a name = "I9"></a>
This global variable contains the class of all finite supersoluble groups. It
is a subgroup closed saturated formation.
<p>
<a name = "SSEC001.4"></a>
<li><code>AbelianGroups V</code>
<p>
<a name = "I10"></a>
<a name = "I11"></a>
<a name = "I12"></a>
is the class of all abelian groups. It is a subgroup closed formation.
<p>
<a name = "SSEC001.5"></a>
<li><code>AbelianGroupsOfExponent(</code><var>n</var><code>) F</code>
<p>
<a name = "I13"></a>
<a name = "I14"></a>
<a name = "I15"></a>
returns the class of all abelian groups of exponent dividing <var>n</var>,
where <var>n</var> is
a positive integer. It is always a subgroup-closed formation.
<p>
<a name = "SSEC001.6"></a>
<li><code>PiGroups(</code><var>pi</var><code>) F</code>
<p>
<a name = "I16"></a>
constructs the class of all <var>pi</var>-groups. <var>pi</var> may be a non-empty class or a
set of primes. The result is a subgroup-closed saturated Fitting formation.
<p>
<a name = "SSEC001.7"></a>
<li><code>PGroups(</code><var>p</var><code>) F</code>
<p>
<a name = "I17"></a>
returns the class of all <var>p</var>-groups, where <var>p</var> is a prime. The result is a
subgroup-closed saturated Fitting formation.
<p>
<p>
<h2><a name="SECT002">6.2 Pre-defined projector functions</a></h2>
<p><p>
<a name = "SSEC002.1"></a>
<li><code>NilpotentProjector(</code><var>grp</var><code>) A</code>
<p>
<a name = "I18"></a>
This function returns a projector for the class of all finite nilpotent
groups. For a definition, see <a href="CHAP004.htm#SSEC002.3">Projector</a>. Note that the nilpotent projectors
of a finite soluble group equal its a Carter subgroups, that is, its
self-normalizing nilpotent subgroups.
<p>
<a name = "SSEC002.2"></a>
<li><code>SupersolubleProjector(</code><var>grp</var><code>) A</code>
<a name = "SSEC002.2"></a>
<li><code>SupersolvableProjector(</code><var>grp</var><code>) A</code>
<p>
These functions return a projector for the class of all finite supersoluble
groups. For a definition, see <a href="CHAP004.htm#SSEC002.3">Projector</a>.
<p>
<p>
<h2><a name="SECT003">6.3 Pre-defined sets of primes</a></h2>
<p><p>
<a name = "SSEC003.1"></a>
<li><code>AllPrimes V</code>
<p>
<a name = "I19"></a>
<a name = "I20"></a>
labelAllPrimesrelax
is the set of all (integral) primes. This should be
installed as value for <code>Characteristic(</code><var>grpclass</var><code>)</code> if the group class
<var>grpclass</var> contains cyclic groups of prime order <var>p</var> for arbitrary primes <var>p</var>.
<p>
<p>
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<address>CRISP manual<br>August 2025
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