A trait with many of the same methods as Seq, but not actually a Seq itself. This is necessary because Seq defines "equals" based on same contents, but all variables must have equals based on identity.
(Changed in version 2.9.0) The behavior of scanRight has changed. The previous behavior can be reproduced with scanRight.reverse.
(Changed in version 2.9.0) transpose throws an IllegalArgumentException if collections are not uniformly sized.