@Kishikawa Katsumi,
/usercode/main.swift:6:1: error: type 'X<T>' does not conform to protocol 'B' extension X: C where T: Equatable { } ^ /usercode/main.swift:3:10: note: type 'X<T>' does not conform to inherited protocol 'B' protocol C: B { } ^ Swift version 4.1 (swift-4.1-RELEASE) Target: x86_64-unknown-linux-gnu