Function: idealaddtoone
Section: number_fields
C-Name: idealaddtoone0
Prototype: GGDG
Help: idealaddtoone(nf,x,{y}): if y is omitted, when the sum of the ideals
 in the number field K defined by nf and given in the vector x is equal to
 Z_K, gives a vector of elements of the corresponding ideals who sum to 1.
 Otherwise, x and y are ideals, and if they sum up to 1, find one element in
 each of them such that the sum is 1

