What happens when you convert RGB to CMYK?

The underlying color model in Photoshop is neither RGB nor CMYK but LAB. It has the widest gamut, which means it can hold more color values than any other model. Of the two other models, RGB has more color values than CMYK does. When you convert from RGB to CMYK, the program first "maps" the RGB values into the LAB colorspace. It then maps the LAB values into the CMYK colorspace. Now, for REAL entertainment...take a pure RGB blue, or a pure RGB green, and attempt to map it into CMYK colorspace. It doesn't work at all. Red maps fine, but the other two go straight to hell.