If as many odd numbers as we please be added together, and their multitude be even, the whole is even.
many_odd_numbers()
prove/ A E / is even
construct Let as many odd numbers as we please, / A B /, / B C /, / C D /, / D E /, even in multitude, be added together
∵odd_number_divisible_defassert each of the numbers/ A B /, / B C /, / C D /, / D E / is odd, if an unit be subtracted from each, each of the remainders will be even