custom cases tactic

test/cases.lean

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+import Game.Tactic.Cases
+import Game.MyNat.Inequality
+
+namespace MyNat
+
+example (P Q : Prop) (h : P ∨ Q) : False := by
+  cases h with hp hq
+  · sorry -- hp : P
+  · sorry -- hq : Q
+
+example (a b : ℕ) (h : a ≤ b) : False := by
+  cases h with c hc
+  -- hc: b = a + c
+  sorry
+
+-- not working yet
+example (a : ℕ) : a = a := by
+  cases a with d
+  -- get MyNat.zero because we used rec not rec' :-(
+  · sorry
+  · sorry