DOC: fix typo in scale resolve user guide
@@ -76,7 +76,7 @@ each layer.
In this case the axis colors act as a pseudo-legend. Alternatively if you want
a legend the :ref:`user-guide-filter-transform` and
-:ref:`user-guide-fold-transform` be applied. Legends are only created in
+:ref:`user-guide-fold-transform` must be applied. Legends are only created in
Vega-Lite to represent an encoding.
.. altair-plot::
