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https://github.com/PentahoCommunityMeetup2015/info/blob/master/README.md
Registration can be done here:
https://www.eventbrite.com/e/pentaho-community-meeting-tickets-16994065708
And registration for the hackathon here:
http://www.meetup.com/Pentaho-London-User-Group/events/222548597/
And a blog can be found here:
https://dankeeley.wordpress.com/2015/06/04/pentaho-community-meetup-2015/