string comparsion "inf"

Hi all, I got a problem comparing the string "inf" with another in PHP3. It is used as File-Extention for information-files on our system. When comparing the following all works fine and the expected result is given: "otto" = "karl" =>0 "otto" = "otto" =>1 "otto"! = "karl" =>1 "otto"! = "otto" =>0 The following problem occurs when comparing the string "inf": "inf" = "otto" =>0 correct result "inf" = "inf" =>0 incorrect result!!!! expected 1 "inf" != "otto" =>1 correct result "inf" != "inf" => 1 incorrect result!!! expected: 0 Does anybody have any idea what´s wrong with the string "inf"? It is not an reserved word. Tahnks in advance Marco