An ADElphabet

Some things involved in the ADE affair.

A is for asymptotically locally Euclidean space B is for binary polyhedral group C is for Clifford algebra, or cluster algebra D is for Du Val singularity E is for eigenvalue, or exceptional Lie algebra F is for Fischer group G is for generalized line graph H is for Hurwitz units I is for icosahedral group J is for Jacobi identity K is for Klein j-invariant L is for Lie group M is for Monstrous Moonshine N is for Niemeier lattices O is for orbifold P is for Perron–Frobenius theorem Q is for quaternions R is for reflection groups S is for spinor, or swallowtail catastrophe T is for triangle property, or trinity U is for unitary group V is for Vladimir Arnold W is for Weyl group XYZ are the coordinates of a vector