Re: [Haskell-cafe] What is a "simple pattern binding"?

I thought "no type signature" meant no type signature inside b1.

No, it means no type signature for the variable.

Otherwise, you are saying nothing could depend on a binding with a type signature. By that logic, there can be no mutual dependence, and so every declaration with a type signature is its own (singleton) declaration group.

A pattern binding can bind more than one variable. If all the variables bound by a binding have type signatures, that binding is indeed a singleton declaration group.