Thanks yes! OK so we say
A=[ai,bi)U[a(i+1),b(i+1)U...U[ar,br)
Ac = omega/A
Then 3 is now easy
A=[ai,bi)U[a(i+1),b(i+1)U...U[ar,br)
B=[aj,bj)U[a(j+1),b(j+1)U...U[as,bs)
so AUB = [ai,bi)U[a(i+1),b(i+1)U...U[ar,br)U[aj,bj)U[a(j+1),b(j+1)U...U[as,bs)
AUB=[ak,bk)U[a(k+1),b(k+1)U...U[at,bt)...