Material for further reading :

About alert: http://neapolitanclub.altervista.org/eng/ev-eng/notes-alerting-internet.html

About Multi: http://jazclass.aust.com/bridge/br29.htm and against Multi: http://neapolitanclub.altervista.org/eng/tackling-the-multicolor-the-cento-torri-defence.html

About signalling. Suggested reading: http://neapolitanclub.altervista.org/eng/defensive-signal-part-one.html and http://neapolitanclub.altervista.org/eng/defensive-signal-part-two.html

About a couple of weak opening systems : http://clairebridge.com/textes/MagicDiamond.pdf and https://en.wikipedia.org/wiki/Säffle_Spade