English
Exists P is defined as the existence of a matrix X such that P(X) holds; structurally defined by recursion on m and n.
Русский
Существование предиката над матрицами определяется как существование матрицы X such that P(X) holds; структура задаётся рекурсивно по m и n.
LaTeX
$$Exists P$$
Lean4
/-- `∃` with better defeq for `∃ x : Matrix (Fin m) (Fin n) α, P x`. -/
def Exists : ∀ {m n} (_ : Matrix (Fin m) (Fin n) α → Prop), Prop
| 0, _, P => P (of ![])
| _ + 1, _, P => FinVec.Exists fun r => Exists fun A => P (of (Matrix.vecCons r A))