[Gmsh] How to enclose a point in a surface ?

[philippe carette]

Hello,
I want to impose a Dirichlet condition on a solid.

So, i want to enclose points in the boundary, in view to declare the 
movings with those points.

How can i do that ?
Duplicate points, and translate one very close is a solution to get lines.
But it's not very neat, and i should declare 2 moving, instead only one.
perhaps, there exits some tip to do this task ?

Thanks in advance for respond.