Removing extra space.

optimade.rst

@@ -2739,7 +2739,7 @@ space\_group\_symmetry\_operation\_xyz
 - **Description**: a list of symmetry operations given as general positions `x,y,z` coordinates in algebraic form.
   Each symmetry operation is described as a string representing the symmetry operation in Jones' faithful representation (Bradley & Cracknell, 1972:pp. 35--37), adapted for computer string notation.
   The letters `x`, `y` and `z` that are typesetted with overbars in printed text represent coordinates values multiplied by -1 and are encoded as `-x`, `-y` and -`z`, respectively.
-  The syntax of the strings representing symmetry operators MUST conform to regular expressions given in appendix `The Symmetry Operator Regular Expressions` _.
+  The syntax of the strings representing symmetry operators MUST conform to regular expressions given in appendix `The Symmetry Operator Regular Expressions`_.
   The interpretation of the strings MUST follow the conventions of the IUCr CIF code dictionary (IUCr, 2023).
   In particular, this property MUST explicitly provide all symmetry operations needed to generate all the atoms in the unit cell from the atoms in the asymmetric unit, for the setting used.
   The identity operation `x,y,z` MUST be always present.