user = User.objects.get(email=email)

        except User.DoesNotExist:

            # eventually we can invite them but for now assume they are

            # already on the site

            raise forms.ValidationError(mark_safe("no account with email address <b>%s</b> found on this conference site" % escape(email)))

        state = self.team.get_state_for_user(user)

        if state in ["member", "manager"]:

            raise forms.ValidationError("user already in team")

        if state in ["invited"]:

            raise forms.ValidationError("user already invited to team")

        self.user = user

        self.state = state

        return cleaned_data

    def invite(self):

        if self.state is None:

            Membership.objects.create(team=self.team, user=self.user, state="invited")

        elif self.state == "applied":

            # if they applied we shortcut invitation process