Hi Candlestick, having formed a copy grid, examine cells of the original grid according to the whereabouts of certain cells in the copy grid. It is a form of coding as indicated by the theme word.
Jazzlover42, 11a Wrong hero, this one had a problem with his heel. 3d as Bazotto suggests...
Hi Fgsltw, 6 : R(epublican), acts, with is in; 11a : starts of words - an architectural feature, also the name of a place where Zeno would speak at; 17a is abbreviation of the old term for a system of wrights and measures. French to have; 18a : Name of Austrian oil painter, exploit as in drink obtained from cows