This is a sub-release of 3.1. Some of the new facilities are experimental and may be changed or removed in the next full release of SDML. Therefore you are recommended to continue with 3.1 unless you need the new facilities. This sub-release is implemented in release 2.5.1 of VisualWorks, so you may need to upgrade to a newer VisualWorks "object engine" in order to use it. This sub-release provides: a) some user interface extensions, which use agents to represent windows or panes on the screen, and which use a new time level representing "real time". These facilities have not yet been fully implemented and are likely to change. b) list types, so that the types of list elements can be specified in syntax diagrams. c) a "sole" facility, which enables the user to specify in a syntax diagram that there can only be one instance of a type (at any particular time for the same agent) as an argument of a clause. An error will result if it is attempted to assert a clause that violates such a constraint. However, this facility is currently only implemented for forward chaining predicates where all the arguments are defined as "sole".