Adds new contexts to the agenda.
A list of context names.
The given list of contexts in context-list is placed on top of the agenda (the context stack). The current context is not changed. It is an error if the named contexts do not exist.
If context-list contains variables, then they must be already bound.
(context (?x ?y)) ; if ?x ?y bound to context names
KnowledgeWorks and Prolog User Guide (Unix version) - 24 Mar 2017