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acting: add WeakInverse method for all types #936

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acting: add WeakInverse method for all types #936

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26 changes: 26 additions & 0 deletions gap/main/setup.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -1268,3 +1268,29 @@ InstallMethod(WeakInverse, "for a partial perm",

InstallMethod(WeakInverse, "for a bipartition",
[IsBipartition], Star);

InstallMethod(WeakInverse, "for a matrix over ff",
[IsMatrixObjOverFiniteField], RightInverse);

InstallMethod(WeakInverse, "for a McAlister triple semigroup element",
[IsMcAlisterTripleSemigroupElement], INV);

InstallMethod(WeakInverse, "for a Rees 0-matrix semigroup",
[IsReesZeroMatrixSemigroupElement],
function(x)
local R, mat, i, j, k, l;

R := ReesMatrixSemigroupOfFamily(FamilyObj(x));
if IsMultiplicativeZero(R, x) then
return x;
fi;

mat := Matrix(R);
i := x[1];
j := x[3];

k := First(Rows(R), k -> mat[j][k] <> 0);
l := First(Columns(R), l -> mat[l][i] <> 0);

return RMSElement(R, k, mat[j][k] ^ -1 * x[2] ^ -1 * mat[l][i] ^ -1, l);
end);