sphere sph 1
mkface f sph 0 2 0 pi/2
explode f w
nurbsconvert w f_1
sphere sph 0.1 0.1 0.1 1
getanasurf res w sph 1.e-3 sph
if {[isdraw res]} {
  set log [dump res]
  if { [regexp {SphericalSurface} $log ] != 1 } {
     puts "Error: surface is not a spherical surface"
  }
} else {
  puts "Error: required surface is not got"
}