Let
I1, I2 be ideals of R and J1, J2 be ideals of S. Show that (I1 +
I2)^extension= I1^extension + I2^extension where I1, I2 are
contained in R
|^e
is defined as the extension of I to S: Let R and S be commutatuve
ring and f:R to S be a ring homomorphism. For each ideal I of R,
the ideal f(I)S of S generated by f(I) is the extension of I to
S.