test: add new induction tactic tests

tests/lean/run/induction1.lean

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+@[recursor 4]
+def Or.elim2 {p q r : Prop} (major : p ∨ q) (left : p → r) (right : q → r) : r :=
+Or.elim major left right
+
+new_frontend
+
+theorem tst0 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h;
+  { apply Or.inr; assumption };
+  { apply Or.inl; assumption }
+end
+
+theorem tst1 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h with
+  | inr h2 => Or.inl h2
+  | inl h1 => Or.inr h1
+end
+
+theorem tst2 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h using elim2 with
+  | left _  => Or.inr $ by assumption
+  | right _ => Or.inl $ by assumption
+end
+
+theorem tst3 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h using elim2 with
+  | right h => Or.inl h
+  | left h  => Or.inr h
+end
+
+theorem tst4 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h using elim2 with
+  | right h => ?myright
+  | left h  => ?myleft;
+  case myleft  { exact Or.inr h };
+  case myright { exact Or.inl h };
+end
+
+theorem tst5 {p q : Prop } (h : p ∨ q) : q ∨ p :=
+begin
+  induction h using elim2 with
+  | right h => Or.inl ?myright
+  | left h  => Or.inr ?myleft;
+  case myleft  assumption;
+  case myright exact h;
+end