typo

Author: Froussios

Part 2 - Sequence Basics/2. Reducing a sequence.md

@@ -6,7 +6,7 @@ Most of the operators here will be familiar to anyone who has worked with Java's
 
 ### Marble diagrams
 
-This is an appropriate time to introduce to concept of marble diagrams. It is a popular way of explaining the operators in Rx, because of their intuitive and graphical nature. They are present a lot in the documentation of RxJava and it only makes sense that we take advantage of their explanatory nature. The format is mostly self-explanatory: time flows left to right, shapes represent values, a slash is a onCompletion, an X is an error. The operator is applied to the top sequence and the result is the sequence below.
+This is an appropriate time to introduce to concept of marble diagrams. It is a popular way of explaining the operators in Rx, because of their intuitive and graphical nature. They are present a lot in the documentation of RxJava and it only makes sense that we take advantage of their explanatory nature. The format is mostly self-explanatory: time flows left to right, shapes represent values, a slash is an onCompletion, an X is an error. The operator is applied to the top sequence and the result is the sequence below.
 
 ![](https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/legend.png)