In 1949 H.-E.Richert proved (1) that every positive integer typeset structure is a sum of distinct primes. For more information please look at (2), and (3).
However, if you consider $ n = 11 $, you will see that you can't express it as a sum of distinct prime numbers.
Is there an error in Richert’s theorem?
(1): Richert, H. E. (1949). Über Zerfällungen in ungleiche Primzahlen. (German). Math. Z., 52, 342-343.