RAQ/gap/byconj.gi

# byconj.gi RAQ Implementation of quandles by conjugation

InstallMethod(ConjugatorFamily, "for a family",
  [IsFamily],
  function(fam)
    local F;
    # Does GAP provide any way to get at the name of a family other than
    # fam!.NAME ?
    F := NewFamily(Concatenation("ConjugatorFamily(", fam!.NAME, ")"),
                   IsConjugatorObject);
    F!.ConjType := NewType(F, IsDefaultConjugatorObject);
    return F;
end);

ConjugatorType@ := obj -> ConjugatorFamily(FamilyObj(obj))!.ConjType;


InstallMethod(ConjugatorObj,
  "for a mult element that allows quotients (and should be assoc)",
  [IsMultiplicativeElementWithInverse],
  obj -> Objectify(ConjugatorType@(obj), Immutable(obj))
);

## Printing and viewing
InstallMethod(String, "for conjugator objects",
  [IsDefaultConjugatorObject],
  obj -> Concatenation("ConjugatorObj( ", String(obj![1]), " )")
);

InstallMethod(ViewString, "for conjugator objects",
  [IsDefaultConjugatorObject],
  obj -> Concatenation("^", ViewString(obj![1]), ":")
);

InstallMethod(UnderlyingMultiplicativeElement, "for a conjugator object",
  [IsDefaultConjugatorObject],
  obj -> obj![1]
);

InstallMethod( \=, "for two conjugator objects",
  IsIdenticalObj,
  [IsDefaultConjugatorObject, IsDefaultConjugatorObject],
  function(l,r) return l![1] = r![1]; end
);

InstallMethod( \<, "for two conjugator objects",
  IsIdenticalObj,
  [IsDefaultConjugatorObject, IsDefaultConjugatorObject],
  function(l,r) return l![1] < r![1]; end
);

InstallMethod( \*, "for two conjugator objects",
  IsIdenticalObj,
  [IsDefaultConjugatorObject, IsDefaultConjugatorObject],
  function(l,r) return ConjugatorObj(LeftQuotient(l![1],r![1])*l![1]); end
);

InstallOtherMethod(LeftQuotient, "for two conjugator objects",
  IsIdenticalObj,
  [IsDefaultConjugatorObject,IsDefaultConjugatorObject],
  function(l,r) return ConjugatorObj((l![1]*r![1])/l![1]); end
);

InstallMethod(ConjugationQuandle, "for a group",
  [IsGroup and IsFinite],
  function(G)
    local fam, elts, Q;
    fam := CollectionsFamily(ConjugatorFamily(ElementsFamily(FamilyObj(G))));
    # Question: how do we feasibly determine a set of generators of
    # Conj(G) from a set of generators of G, so that we can handle infinite
    # conj-quandles here?
    elts := List(Elements(G), g -> ConjugatorObj(g) );
    # What we would like to do is
    #   return AsLeftQuandle[NC?](elts);
    # but that's NIY.
    Q := LeftQuandleNC(fam, elts);
    # We know that elts was actually closed under * and LeftQuotient, and
    # since we are in a method only for finite groups, ergo Q is finite:
    SetIsFinite(Q, true);
    return Q;
end);

## Methods that are easier in conjugator quandles:

InstallMethod(GeneratorsOfMagma,
  "for a quandle generated by conjugator objects",            
  [IsLeftQuasigroup and HasGeneratorsOfLeftQuasigroup and
   IsConjugatorObjectCollection],
  function(Q)
    local gens, invgens;
    # idea: ^g^-1: * ^h: = ^g: \ ^h:, so the generators of the quasigroup
    # together with their inverses generate the quandle as a magma.
    gens := GeneratorsOfLeftQuasigroup(Q);
    invgens := Set(gens, g -> Inverse(g));
    UniteSet(invgens, gens);
    return invgens;
end);