4. Given two CFG's G1 and G2, how can we build a CFG to generate the union? fully describe the resulting grammar (6) b) how do we know that cfl are not closed under intersection? (5) show how a pda transition like (see diagram below) would be implemented if only one symbol can be pushed at a time? (4) 4. Given two CFG's G1 and G2, how can we build a CFG to generate the union? fully describe the resulting grammar (6) b) how do we know that cfl are not closed under intersection? (5) show how a pda transition like (see diagram below) would be implemented if only one symbol can be pushed at a time? (4)