Type Alias FunctionRT<From, To>

FunctionRT: fn extends From
    ? _FunctionRTUnknown
    : fn extends To
        ? _FunctionRTUnknown
        : Parameters<From>["length"] extends Parameters<To>["length"]
            ? _EQ & { type: "function" }
            : {
                argCount: Subtract<
                    Parameters<From>["length"],
                    Parameters<To>["length"],
                >;
                result: "diff-arg";
                type: "function";
            }