2-part invention in counterpoint

1 hour ago, Fermata said:

Well, it is a fugue subject that begins on the 4th degree of the scale.
And in fact, fugue subjects can begin on any scale degree, not only the tonic or dominant (see examples below).

I suppose a subject beginning on the 4th is as about as allowed as an interrupted cadence in a chorale. You can find them every now and then but they are so exceedingly rare in the oeuvre. This fugue would also be the second part of an overture, following a perfect cadence in F. So the issue of your subject establishing the key centre is no longer significant. If one were to compose a standalone piece, the 4th would most certainly be raised to a 5th, then un-raised in later entries as tonal answers.

1 hour ago, Fermata said:

I'm sorry, but this is neither invertible nor correct counterpoint.

How embarassing. Fixed below!