docs: def set(self, names):
          """Return a variable set of the given names in the namespace.
  
          >>> v = prob.namespace(name='v')
          >>> v.define([1, 2, 5], lower=0, upper=10)
          >>> prob.add_linear_constraints(v.set([1, 2]) >= 4)
          """
          return self._problem.set((self, name) for name in names)