2a Extremely cautious having disrobed outside house (5) A???? 17a Course on Gershwin's prime pieces around noon (5) ...starts P/Q/R/S 1d Artist promoting his second rubbish improvs (6) ..starts with...
Stuck in SW corner ...consequently can't fill in the unclued 56a......and the highlighting required.. there is an extra letter in the wordplay... 50d Hang pleb in short uprising (3) LO? "R" possibly...
There are misprints in some clues ...also some clashes in the grid....so crossers may not help.. 1a Does poorly after accompanist's treated (8) 10a Greek nymph briefly goes back after a coloured hat...