theorem Th51: :: STIRL2_1:51

for n being Nat holds
( n choose 1 = n & n choose 2 = (n * (n - 1)) / 2 & n choose 3 = ((n * (n - 1)) * (n - 2)) / 6 & n choose 4 = (((n * (n - 1)) * (n - 2)) * (n - 3)) / 24 )