Dahon Speed Uno. Main frame hard to fold
The main frame hinge is made to have adjustable tension. A little lubrication on moving parts is a good thing.
The manual Dahon publishes is a one-size-fits-all manual with instructions for adjusting a variety of frame hinges starting on page 14.
Here is a review of the Dahon Speed Uno that goes into great detail on how to operate the bicycle along with videos of folding and unfolding.