KernelFieldHomomorphism( hom )
KernelFieldHomomorphism returns the kernel of the field homomorphism
hom.
Because the kernel must be a ideal in the source and it can not be the full source (because we require that the one of the source is mapped to the one of the range), it must be the trivial ideal. Therefor the kernel of every field homomorphism is the set containing only the zero of the source.
GAP 3.4.4