F = ab + bc + ca
G = (a + b)(b + c)(c + a)
= (b + ac)(c + a) Distributive Law [ (x+y)(x+z) = x + yz]
= bc + ba + ac*c +ac*c
= bc+ ba +ac +ac
= ab + bc + ca
NAND- NAND Realization is Equivalent to AND-OR Realization.
H = NAND [NAND(a,b), NAND(b,c), NAND(c,a)]
= OR[AND(a,b), AND(b,c), AND(c,a)]
= OR[ab, bc, ca]
= ab + bc + ca
So, F,G,H are Equivalent.