fix: export is_subfield_normal and principal_subfields (#1657)

Closes #1656

src/NumField/NfAbs/NfAbs.jl

@@ -470,7 +470,7 @@ end
       is_subfield_normal(K::AbsSimpleNumField, L::AbsSimpleNumField) -> Bool, NumFieldHom{AbsSimpleNumField, AbsSimpleNumField}
 
 Returns `true` and an injection from $K$ to $L$ if $K$ is a subfield of $L$.
-Otherwise the function returns "false" and a morphism mapping everything to 0.
+Otherwise the function returns `false` and a morphism mapping everything to `0`.
 
 This function assumes that $K$ is normal.
 """
@@ -481,7 +481,6 @@ function is_subfield_normal(K::AbsSimpleNumField, L::AbsSimpleNumField)
   end
   b, prim_img = _issubfield_normal(K, L)
   return b, hom(K, L, prim_img, check = false)
-
 end
 
 ################################################################################

src/NumField/SimpleNumField/Subfields.jl

@@ -75,6 +75,17 @@ end
 
 Return the principal subfields of $L$ as pairs consisting of a subfield $k$
 and an embedding $k \to L$.
+
+# Examples
+
+```jldoctest
+julia> Qx, x = QQ["x"];
+
+julia> K, a = number_field(x^8 - x^4 + 1);
+
+julia> length(principal_subfields(K))
+8
+```
 """
 function principal_subfields(K::SimpleNumField)
   v = get_attribute(K, :principal_subfields)

src/exports.jl

@@ -557,6 +557,7 @@ export is_snf
 export is_split
 export is_squarefree
 export is_subfield
+export is_subfield_normal
 export is_subgroup
 export is_sublattice
 export is_sublattice_with_relations
@@ -737,6 +738,7 @@ export prime_ideals_up_to
 export primes
 export primitive_closure
 export principal_generator
+export principal_subfields
 export pselmer_group
 export pselmer_group_fac_elem
 export pseudo_basis