(Gresham, OR)  --  Police in Gresham are looking for a man who robbed an eleven-year-old boy with a knife.  It happened yesterday afternoon as the boy was walking in front of a Safeway store in the 47-hundred block of Southwest 11th Street.  Authorities say the boy wasn't injured in the robbery.  They're now looking for a man in his 30s who had on a dark hoodie and blue jeans.