Mathieu groupoid
GROUPOID, ACTING ON A SET OF 13 ELEMENTS, SUCH THAT THE STABILIZER OF EVERY POINT IS THE MATHIEU GROUP M₁₂
Mathieu pseudogroup; Mathieu groupoid M13; Mathieu group M13; Conway's M13
In mathematics, the Mathieu groupoid M13 is a groupoid acting on 13 points such that the stabilizer of each point is the Mathieu group M12. It was introduced by and studied in detail by .