Fix documentation build issues

when building PDF manuals. I am not sure why I need to protect ≤ in a math
environment but I checked that this looks good in the PDF output like that.

src/doc/en/reference/valuations/index.rst

@@ -81,9 +81,9 @@ Internally, all the above is backed by the algorithms described in
 ``K.valuation(x - 4)`` to the field `L` above to outline how this works
 internally.
 
-First, the valuation on `K` is induced by a valuation on `\Q[x]`. To construct
-this valuation, we start from the trivial valuation on `\Q` and consider its
-induced Gauss valuation on `\Q[x]`, i.e., the valuation that assigns to a
+First, the valuation on `K` is induced by a valuation on `\QQ[x]`. To construct
+this valuation, we start from the trivial valuation on `\\Q` and consider its
+induced Gauss valuation on `\\Q[x]`, i.e., the valuation that assigns to a
 polynomial the minimum of the coefficient valuations::
 
     sage: R.<x> = QQ[]

src/sage/rings/valuation/valuation.py

@@ -1052,7 +1052,7 @@ class MacLaneApproximantNode(object):
     relevant, everything else are caches/debug info.) The boolean ``ef``
     denotes whether ``v`` already has the final ramification index E and
     residue degree F of this approximant.  An edge V -- P represents the
-    relation ``P.v ≤ V.v`` (pointwise on the polynomial ring K[x]) between the
+    relation ``P.v`` `≤` ``V.v`` (pointwise on the polynomial ring K[x]) between the
     valuations.
 
     TESTS::