15a. European chap following upright type round university (9) R???A?I?N 51d. Old dramatist's colleague executed outside back of Mountjoy (4) ?Y?Y 54a. Birch extending over head of remote mountain lake (4) T?R? - Is it TARN? 47d. Young people writing about modern soldiers (6) ?I?O?S - I think MINORS but can't work out why.