Sew up the shoulder line. Sew up the side.
Sew the under collar to the body (a-b-c-b-a).
Sew up the facing (c'-f).
Sew the collar to the facing (a'-b'-c'-b'-a').
Sew up the collar and the under collar.
Sew the facing to the body (a-d-e-d-a). Trim the seam allowance of the collar and lapel to 0.1 - 0.3 cm.
Turn inside out.
Sew the seam allowance of the neck (a-b-c-b-a) to the seam allowance of the neck (a'-b'-c'-b'-a'). Any stitch is OK. It is hidden.
Stitch the facing to the seam allowance of the shoulder. (b'-g)
Sew up the sleeve. Hem the cuff with slip stitches.
Sew the sleeve to the body.
Slip-stitch the hem of the body (h-i-h).
Fold the collar. Make a buttonhole. Sew a button.