Allow 'undef' only in operands.
Allow 'undef' only in operands.

rutgers-apl/alive-loops,chubbymaggie/alive,nunoplopes/alive,rutgers-apl/alive-loops,rutgers-apl/alive-loops,rutgers-apl/alive-loops,nunoplopes/alive,chubbymaggie/alive,chubbymaggie/alive,nunoplopes/alive,nunoplopes/alive,chubbymaggie/alive