sets, maps and lists are now homogeneous.
Lists by extension now require the "list" keyword, like sets and
maps. Semicolons needed, instead of commas.
New syntax for lists: `list [e_1; e_2; ...; e_n]`.
The empty list can now be denoted either by `list []` or `list end` or
`nil'.
Both `list` and `nil` are new keywords. Lists can also be denoted
without brackets, as sets and maps: `list e_1; e_2; ...; e_n end`.
The extension for maps follows the extension for sets: `map [b_1; b_2;
...; b_n]` or `maps b_1; ...; b_n end`.
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