Description: Amagma is a set equipped with an everywhere defined internal
operation. Definition 1 in BourbakiAlg1 p. 1, or definition of a
groupoid in section I.1 of Bruck p. 1. Note: The term "groupoid" is
now widely used to refer to other objects: (small) categories all of
whose morphisms are invertible, or groups with a partial function
replacing the binary operation. Therefore, we will only use the term
"magma" for the present notion in set.mm. (Contributed by FL, 2-Nov-2009)(Revised by AV, 6-Jan-2020)