IsField( D )
IsField returns true if the object D is a field and false
otherwise.
Field Records). So, for example, a matrix group may in fact be a field, yet
IsField would return false.
gap> IsField( GaloisField(16) );
true
gap> IsField( CyclotomicField(9) );
true
gap> IsField( rec( isDomain := true, isField := true ) );
true # it is possible to fool 'IsField'
gap> IsField( AsRing( Rationals ) );
false # though this ring is, as a set, still 'Rationals'
GAP 3.4.4