f [x] = / [Gn] f [x] = / / [ ] / [Gn] f [x] = / / / [Gn] f [x] = / / [ ] / [Gn] f [x] = / / [ ] / / [Gn] [-] [Gn] f [x] = / / [ ] / / [Gn] f [x] = / / [ ] / / [Gn] = [Gn] = ...