Linear structures on measured geodesic laminations

The space ML(F) of measured geodesic laminations on a given closed hyperbolic surface F has a canonical linear structure arising in fact from different sources in 2-dimensional hyperbolic (earthquake theory) or complex projective (grafting) geometry as well as in (2+1) Lorentzian one (globally hyperbolic spacetimes of constant curvature). We investigate this linear structure, by showing in particular how heavily it depends on the geometric structure of F, whle to many other extens ML(F) depends only on the topology of F. This is already manifest when we describe in geometric terms the sum of two measured geodesic laminations in the simplest non trivial case of two weighted simple closed geodesics that meet each other at one point.