Can a writeable stream be piped to either a readable or wirtable stream

Can a writeable stream be piped to either a readable or wirtable stream

code:
a.pipe(b).pipe(c).pipe(d);
Im node newbie. I read that for piping, the source should be a readable
stream and destination should be a writeable stream.
If you see the above code, my assumption is that 'a' is readable stream,
'b' is writable stream. If 'b' is writable stream how is it possible to
pipe it further?
how the 'b' writeable stream is piped to 'c'?
Streams and Buffers is being difficult to understand. Any good
documentation to read?