sfera[u_,v_]:={Cos[u]Cos[v],Sin[u]Cos[v],Sin[v]};

trot[u_,v_]:={(1+Sin[v])Cos[u],(1+Sin[v]) Sin[u],v};

srot[f_][u_,v_]:={f[v]*Cos[u],f[v]* Sin[u],v};

toro[r_][u_,v_]:={(r+Sin[u])Cos[v],(r+Sin[u]) Sin[v],Cos[u]};

sbucciamolt[sup_,c_,k_,vm_,vM_]:=Show[{
ParametricPlot3D[sup,{u,vm/c-2k*Pi,vM/c},{v,vm,vM},RegionFunction->Function[{x,y,z,u,v},c*u<v<c*(u+2k*Pi)],PlotPoints->50,Mesh->None,Boxed->False,Axes->None],
ParametricPlot3D[sup/. v->c*u,{u,vm/c,vM/c},PlotStyle->{Thick,Green}],
ParametricPlot3D[sup/. v->c*(u+2k*Pi),{u,vm/c-2k*Pi,vM/c-2k*Pi},PlotStyle->{Thick,Red}]}]

figura=GraphicsRow[{sbucciamolt[sfera[u,v],.1,.5,-Pi/2,Pi/2],sbucciamolt[trot[u,v],.1,.5,-Pi/2,3/2Pi],sbucciamolt[toro[2][u,v],.1,.5,-Pi,Pi]},ImageSize->1200,PlotLabel->"BUON NATALE 2013  ***  Matematica - Curve e Superfici"]

Export["natale2013.pdf",figura]