diff --git a/SimpleCounterexamples/BadInfinities.lean b/SimpleCounterexamples/BadInfinities.lean new file mode 100644 index 0000000..59fe492 --- /dev/null +++ b/SimpleCounterexamples/BadInfinities.lean @@ -0,0 +1,17 @@ +abbrev HasInfinity (α : Type) [LT α] := ∃(inf : α), ∀n, n < inf + +theorem lt_irrefl_imp_no_infinity + (α : Type) [LT α] (irrefl : ∀(n : α), ¬n < n) : ¬HasInfinity α := by + intro h + have ⟨inf, h⟩ := h + have hlt : inf < inf := h inf + exact irrefl inf hlt + + +theorem no_nat_infinity : ¬HasInfinity Nat := + lt_irrefl_imp_no_infinity Nat Nat.lt_irrefl + +theorem no_int_infinity : ¬HasInfinity Nat := + lt_irrefl_imp_no_infinity Nat Nat.lt_irrefl + +-- it's… not difficult to see the pattern