I've completed the puzzle, but the parsing of 25a eludes me. 'Clever remark spread around about something irrational (7).' E?I?R?M. it must be 'epigram'. 'pi' is presumably the 'something irrational', leaving 'e..gram' to parse. 'About' is possibly 'e.g.', leaving 'ram', which is too technical for me to understand. Kind help please.