Table: european_boxing_champs_1947
Columns: event
gold
silver
bronze
4th_place

Question: Who won the gold when Bertil Ahlin Sweden won the silver?
SQL: SELECT "gold" FROM european_boxing_champs_1947 WHERE "silver" = 'bertil ahlin sweden'

Question: Who won the gold when Jules van Dyk Belgium won bronze?
SQL: SELECT "gold" FROM european_boxing_champs_1947 WHERE "bronze" = 'jules van dyk belgium'