Ideals

(... On Tuesday, June 12, 2007 I wrote:
Let I, J be ideals of Z.
If I=(m), J=(n) then I+J=(GCD(m,n)), and I∩J=(LCM(m,n)). ...)

In fact:
Let I, J be ideals of Z.
If I=(m), J=(n) then
- I*J=(m*n)
- I+J=(GCD(m,n)),
- I∩J=(LCM(m,n)),
- I∪J=I+J.

Example:
I = (6) = {..., -18, -12, -6, 0, 6, 12, 18, 24, ...}
J = (4) = {..., -12, -8, -4, 0, 4, 8, 12, 16, ...}

- I*J={..., -48, -24, 0, 24, 48, 72, ...}
- I+J=(GCD(m,n))={..., -4, -2, 0, 2, 4, 6, ...},
- I∩J=(LCM(m,n))={..., -24, -12, 0, 12, 24, 36, ...},
- I∪J=I+J={..., -4, -2, 0, 2, 4, 6, ...}.