[xeonmc]

Why not use the haskell guard syntax?

  A_ij = | 1 if (i,j) ∈ E
         | 0 otherwise
  where
  A ∈ ℝ^(n × n)
  E ∈ { ℤ × ℤ }
  n ∈ ℤ

[yig]

I (speaking as a designer of I Heart LA empathizing with a user) wouldn't have thought to use that character as an approximation of {.