So I was wondering if someone could clear up when you are allowed to omit と when listing things and when it's usually recommended to omit と.
Here are some examples of sentences I found in a book that either omit と altogether or only omit one or two and it's confusing.
今回の旅行ではスペイン、イタリアそしてフランスと、おもに南ヨーロッパを中心に回った。 On this trip I traveled mainly around southern Europe, to Spain, Italy, and France
Why in the above sentence do they omit と after スペイン and イタリア but include it after フランス?
Then in the following sentence they omit と altogether:
夏休みににタイ、マレーシアそれからインドネシアの三カ国を回ってきた。 During the summer vacation I traveled around three countries: Thailand, Malaysia, and Indonesia.
Then in the next one they include と between the first and second noun but leave it between the second and third noun:
初球のクラスは月曜日と水曜日、それから土曜日にやっています。 We have a beginners' class on Mondays, Wednesdays, and Saturdays.
Does this mean that you can choose to use と or leave it out when you like?