Use a proof by contraposition to show that If m2 + n2  is an odd integer, then m is odd or n is odd.
Let p be “if m2 + n2  is an odd integer” and q be “m is odd or n is odd”.
Contrapositive is “If neither m is odd nor n is odd, then m2 + n2  is not odd”
Which is the same as “If m and n are even, m2 + n2 is even”
m2 + n2 = 2km2 + 2kn2		definition of an even number
	= 2(km2 + kn2)		Factor out a 2
	= 2(k’)			k’ = km2 + kn2