1. Introduction  
2. Sample Selection  
2.1. Emission-line spectra of galaxies  
2.2. Analysis of emission-line spectra  
2.3. Final sample of pp-galaxies  
2.4. Classification of the sample  
2.5. Comparison with previous samples  
3. pp-galaxies: SDSS images  
4. Properties of pp-galaxies and asym-NEL galaxies  
5. Conclusions