Forman v. Massachusetts Casualty Insurance

holding that incontestability clauses prohibit challenges to validity of policy but not defenses relating to limitation of coverage | union not estopped when it pled inapplicability of collective bargaining agreement but specifically reserved right to proceed with arbitration if contract did apply | union not estopped when it pled inapplicability of collective bargaining agreement but specifically reserved right to proceed with arbitration if contract did apply | “presumption in favor of arbitrability ... should only be dispelled when the agreement explicitly exempts certain conduct ... or when the terms of the agreement, read as a whole, clearly envision nonarbitrability”