Document ideal interface

Author: emikelsons

docs/make.jl

@@ -90,6 +90,7 @@ makedocs(
                  "field_interface.md",
                  "fraction_interface.md",
                  "module_interface.md",
+                 "ideal_inteface.md",
                  "matrix_interface.md",
                  "map_interface.md",
                  "rand.md",

src/Poly.jl

@@ -3398,7 +3398,7 @@ is_separable(::PolyRingElem)
 
 function is_separable(f::PolyRingElem{<:RingElement})
   # Ford, Separable Algebras, 4.6.1 and 8.3.8
-  return is_one(ideal(base_ring(f), [f, derivative(f)]))
+  return gens(Generic.Ideal(parent(f), [f, derivative(f)])) == [1]
 end
 
 function is_separable(f::PolyRingElem{<:FieldElement})