module P18:

output S1_and_S2,
       S1_and_not_S2,
       not_S1_and_S2,
       not_S1_and_not_S2;

loop
    trap T1 in
        signal S1 in
	    pause;
	    emit S1;
	    exit T1
	||
	    loop
	        trap T2 in
		    signal S2 in
		        pause;
			emit S2;
			exit T2
		    ||
		        loop
			    present S1 then
			        present S2 then
				    emit S1_and_S2
				else
				    emit S1_and_not_S2
				end present
			    else
			        present S2 then
				    emit not_S1_and_S2
				else
				    emit not_S1_and_not_S2
				end
			    end present;
			    pause
			end loop
		    end signal
		end trap
	    end loop
	end signal
    end trap
end loop

end module