fix typo and formatting

docs/src/maths/propagators.md

@@ -4,7 +4,7 @@
 !!! terminology "pushforward and pullback"
 
     _Pushforward_ and _pullback_ are fancy words that the autodiff community recently adopted from Differential Geometry.
-    The are broadly in agreement with the use of [pullback](https://en.wikipedia.org/wiki/Pullback_(differential_geometry)) and [pushforward](https://en.wikipedia.org/wiki/Pushforward_(differential)) in differential geometry.
+    They are broadly in agreement with the use of [pullback](https://en.wikipedia.org/wiki/Pullback_(differential_geometry)) and [pushforward](https://en.wikipedia.org/wiki/Pushforward_(differential)) in differential geometry.
     But any geometer will tell you these are the super-boring flat cases. Some will also frown at you.
     They are also sometimes described in terms of the jacobian:
     The _pushforward_ is _jacobian vector product_ (`jvp`), and _pullback_ is _jacobian transpose vector product_ (`j'vp`).
@@ -20,7 +20,8 @@
  - The **pullback** takes wobbliness information with respect to the function's output, and tells the equivalent wobbliness with respect to the functions input.
 
 #### More formally
-The **pushforward** of ``f`` takes the _sensitivity_ of the input of ``f`` to a quantity, and gives the _sensitivity_ of the output of ``f`` to that quantity
+The **pushforward** of ``f`` takes the _sensitivity_ of the input of ``f`` to a quantity, and gives the _sensitivity_ of the output of ``f`` to that quantity.
+
 The **pullback** of ``f`` takes the _sensitivity_ of a quantity to the output of ``f``, and gives the _sensitivity_ of that quantity to the input of ``f``.
 
 ### Math