Seven countries founded the European Free Trade Association in 1960
The European Free Trade Association, EFTA, was set up by seven countries that stood outside the European Economic Community. They signed its founding treaty, the Stockholm Convention, on 4 January 1960. It is a free trade area: members remove tariffs on trade with each other but, unlike members of a customs union such as the EEC, each keeps its own tariffs on goods from outside. Five of the seven founders later left to join the EEC or the EU, which they entered in 1973, 1986 and 1995. Two founders remain, and EFTA now has four members in all. The list of founders is fixed.
Name them all first. Then split the seven by when, or whether, they left.