[Gmsh] Surface Loops

[John Doe]

I am learning to use gmsh, and I'd like to create a volume from the 6
surfaces of a box.

Right now gmsh is aborting, and I think that it may be because I don't
understand how to order the indices in the surface loop command.  How
are the surfaces supposed to be oriented, and when do I use a negative
index?  At the end of this email are the errors I am  getting.

Thank you,

Juan

Info    : Meshing 2D...
Info    : Meshing surface 1 (Plane, MeshAdapt+Delaunay)
Info    : Meshing surface 2 (Plane, MeshAdapt+Delaunay)
Info    : Meshing surface 3 (Plane, MeshAdapt+Delaunay)
Info    : Meshing surface 4 (Plane, MeshAdapt+Delaunay)
Info    : Meshing surface 5 (Plane, MeshAdapt+Delaunay)
Info    : Meshing surface 6 (Plane, MeshAdapt+Delaunay)
Info    : Mesh 2D complete (1.28808 s)
Info    : Mesh
Info    : Meshing 3D...
Info    : Meshing volume 1 (Netgen)
Info    : Region 1 Face 1, 0 intersect
Info    : Region 1 Face 3, 0 intersect
Info    : Region 1 Face 5, 0 intersect
Info    : Region 1 Face 6, 0 intersect
Info    : Region 1 Face 4, 0 intersect
Info    : Region 1 Face 2, 0 intersect
Info    : CalcLocalH: 2638 Points 0 Elements 4840 Surface Elements
Info    : Check subdomain 1 / 1
Info    : 4840 open elements
Fatal   : ERROR: Edge 1 - 9 multiple times in surface mesh