LEICA calls this the LEICA 50mm SUMMICRON f/2 with near-focusing range.
Laymen also call it the "Dual Range" and "DR."
Many lenses, like the 1957 sample seen here, are marked 5cm instead of 50mm.
7 elements in 5 groups.
Not clear here are that the first two elements are separated by about 1.52mm.
4 elements are of LaK9 glass.