ita; exercise C.1.4 - sum of three numbers in 1..99
ita; exercise C.1.5 - bin(n,k) = n/k bin(n-1,k-1)
ita; exercise C.1.6 - bin(n,k) = n/(n-k) bin(n-1,k)
ita; exercise C.1.7 - bin(n,k) = bin(n-1,k) + bin(n-1,k-1)
ita; exercise C.1.8 - Pascal's trinagle
ita; exercise C.1.9 - Σ(1..n) = bin(n+1,2)
ita; exercise C.1.10 - minimum of bin(n,k)